Add OAuth2 resource server project: JWT validation, JWKS and key rotation

Companion code for the follow-up article. The repository now holds two Maven projects sharing one docs/ tree: jwt-authentication/ the hand-written filter application (unchanged, moved) oauth2-resource-server/ a resource server, a Keycloak compose, and a stub issuer whose JWK Set can be mutated on command The stub exists because Keycloak will not rotate a signing key at a chosen second, report how many times its JWKS endpoint was fetched, or drop a key from the published set on request - and the caching and rotation measurements need all three. The Keycloak run confirms the same code path against a real issuer. Findings captured under docs/output/, all from real runs: * The default validator stack does not check aud. A token minted for another service in the same realm is accepted. * Spring Security builds its JWKSource with refreshAheadCache(false) and rateLimited(false), overriding two of Nimbus's protective defaults, and enables Nimbus caching only when NO Spring cache was supplied - so supplying one removes the five-minute expiry. * A key retired from the JWK Set stops being accepted at t+300s with the default cache, and never with a Spring cache that has no TTL. * 25 tokens carrying an unknown kid produce 25 JWKS fetches at the issuer, through permitAll() endpoints included. * A hyphenated client id in an authorities-claim-expression parses as subtraction; the SpelEvaluationException is swallowed and logged at TRACE. * A clientScopes key in a Keycloak realm import replaces the built-in scopes rather than adding to them. New docs chapters 12-18. README covers both projects. Existing docs and scripts updated for the new paths; no docs/output/ file from the first article moved, so links in the published article still resolve. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_013f7f2XZXrQ6gW3RtZE187t
2026-08-23 11:00:56 +00:00
parent 4a8dab6739
commit 4dc45d5e00
101 changed files with 4087 additions and 64 deletions
--- a/jwt-authentication/pom.xml
+++ b/jwt-authentication/pom.xml
@@ -0,0 +1,74 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+
+  <parent>
+    <groupId>org.springframework.boot</groupId>
+    <artifactId>spring-boot-starter-parent</artifactId>
+    <version>4.1.1</version>
+    <relativePath/>
+  </parent>
+
+  <groupId>com.ankurm</groupId>
+  <artifactId>jwt-auth-demo</artifactId>
+  <version>1.0.0</version>
+  <name>jwt-auth-demo</name>
+  <description>Spring Security 7.1 JWT authentication on Spring Boot 4.1 - runnable companion for ankurm.com</description>
+
+  <properties>
+    <java.version>25</java.version>
+    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+  </properties>
+
+  <dependencies>
+    <dependency>
+      <groupId>org.springframework.boot</groupId>
+      <artifactId>spring-boot-starter-web</artifactId>
+    </dependency>
+    <dependency>
+      <groupId>org.springframework.boot</groupId>
+      <artifactId>spring-boot-starter-security</artifactId>
+    </dependency>
+    <dependency>
+      <groupId>org.springframework.boot</groupId>
+      <artifactId>spring-boot-starter-oauth2-resource-server</artifactId>
+    </dependency>
+    <dependency>
+      <groupId>org.springframework.boot</groupId>
+      <artifactId>spring-boot-starter-validation</artifactId>
+    </dependency>
+
+    <dependency>
+      <groupId>org.springframework.boot</groupId>
+      <artifactId>spring-boot-starter-test</artifactId>
+      <scope>test</scope>
+    </dependency>
+    <!--
+      Spring Boot 4 split the test slices into their own modules. @AutoConfigureMockMvc
+      and @WebMvcTest now live in spring-boot-starter-webmvc-test, and the Spring
+      Security test support arrives via spring-boot-starter-security-test. On Boot 3
+      spring-boot-starter-test alone was enough; on Boot 4 it is not.
+    -->
+    <dependency>
+      <groupId>org.springframework.boot</groupId>
+      <artifactId>spring-boot-starter-webmvc-test</artifactId>
+      <scope>test</scope>
+    </dependency>
+    <dependency>
+      <groupId>org.springframework.boot</groupId>
+      <artifactId>spring-boot-starter-security-test</artifactId>
+      <scope>test</scope>
+    </dependency>
+  </dependencies>
+
+  <build>
+    <plugins>
+      <plugin>
+        <groupId>org.springframework.boot</groupId>
+        <artifactId>spring-boot-maven-plugin</artifactId>
+      </plugin>
+    </plugins>
+  </build>
+</project>
--- a/jwt-authentication/scripts/csrf-demo.sh
+++ b/jwt-authentication/scripts/csrf-demo.sh
@@ -0,0 +1,36 @@
+#!/usr/bin/env bash
+# Reproduces the "permitAll() endpoint still returns 403" failure.
+# Requires: --spring.profiles.active=hs256,csrfon
+set -u
+BASE="${1:-http://localhost:8080}"
+show() {
+  local out
+  out=$(curl -sS -D /tmp/.h -o /tmp/.b -w '%{http_code}' "$@")
+  printf 'HTTP %s\n' "$out"
+  grep -iE '^(www-authenticate|content-type):' /tmp/.h | sed 's/\r$//'
+  [ -s /tmp/.b ] && { python3 -m json.tool < /tmp/.b 2>/dev/null || cat /tmp/.b; echo; }
+}
+hr(){ printf '\n%s\n' "--------------------------------------------------------------------------"; }
+
+echo "=========================================================================="
+echo " jwt-auth-demo - CSRF vs permitAll()"
+echo " app started with: --spring.profiles.active=hs256,csrfon"
+echo "=========================================================================="
+
+hr; echo "# A. The login endpoint is permitAll(). POST it anyway."
+echo "#    403 - and nothing in the authorization rules explains why."
+echo
+show -X POST "$BASE/api/auth/login" -H 'Content-Type: application/json' \
+     -d '{"username":"alice","password":"alice-password"}'
+
+hr; echo "# B. GET on the same permitAll() path family works. Only unsafe methods break."
+echo
+show "$BASE/api/public/ping"
+
+hr; echo "# C. The filter chain, with CsrfFilter present. Count the positions:"
+echo "#    CsrfFilter is 5th, AuthorizationFilter is last. The request never"
+echo "#    reaches the filter that knows about permitAll()."
+echo
+show "$BASE/api/public/filters"
+
+hr; echo "# end"
--- a/jwt-authentication/scripts/curl-transcript.sh
+++ b/jwt-authentication/scripts/curl-transcript.sh
@@ -0,0 +1,112 @@
+#!/usr/bin/env bash
+# Regenerates ../docs/output/curl-transcript-hs256.txt against a running instance.
+# Usage: ./scripts/curl-transcript.sh [base-url]
+set -u
+BASE="${1:-http://localhost:8080}"
+
+hr()  { printf '\n%s\n' "--------------------------------------------------------------------------"; }
+step(){ hr; printf '# %s\n\n' "$1"; }
+
+# Print status line, the security-relevant headers, and the body.
+show() {
+  local out
+  out=$(curl -sS -D /tmp/.h -o /tmp/.b -w '%{http_code}' "$@")
+  printf 'HTTP %s\n' "$out"
+  grep -iE '^(www-authenticate|content-type|set-cookie):' /tmp/.h | sed 's/\r$//'
+  if [ -s /tmp/.b ]; then
+    python3 -m json.tool < /tmp/.b 2>/dev/null || cat /tmp/.b
+    echo
+  fi
+}
+
+jwt_part() { # $1=token $2=0|1  -> pretty-print header or payload
+  echo "$1" | cut -d. -f$(( $2 + 1 )) \
+    | tr '_-' '/+' | sed 's/$/==/' | base64 -d 2>/dev/null \
+    | python3 -m json.tool 2>/dev/null
+}
+
+echo "=========================================================================="
+echo " jwt-auth-demo - curl transcript"
+echo " target : $BASE"
+echo "=========================================================================="
+
+step "1. Public endpoint, no token. permitAll() means the filter chain lets it through."
+show "$BASE/api/public/ping"
+
+step "2. Protected endpoint, no token. 401 - we do not know who you are."
+show "$BASE/api/me"
+
+step "3. Wrong password. Still 401, and the body says nothing about which half was wrong."
+show -X POST "$BASE/api/auth/login" -H 'Content-Type: application/json' \
+     -d '{"username":"alice","password":"wrong-password"}'
+
+step "4. Locked account. 401 with the identical body - no account-state oracle."
+show -X POST "$BASE/api/auth/login" -H 'Content-Type: application/json' \
+     -d '{"username":"locked","password":"locked-password"}'
+
+step "5. Login as alice (ROLE_USER, SCOPE_profile:read)."
+show -X POST "$BASE/api/auth/login" -H 'Content-Type: application/json' \
+     -d '{"username":"alice","password":"alice-password"}'
+ALICE=$(python3 -c "import json;print(json.load(open('/tmp/.b'))['accessToken'])")
+ALICE_REFRESH=$(python3 -c "import json;print(json.load(open('/tmp/.b'))['refreshToken'])")
+
+step "6. What is actually inside that token (base64url decode - no signature check)."
+echo "--- JOSE header ---"
+jwt_part "$ALICE" 0
+echo "--- claims ---"
+jwt_part "$ALICE" 1
+
+step "7. The same protected endpoint, now with the token. 200."
+show "$BASE/api/me" -H "Authorization: Bearer $ALICE"
+
+step "8. alice hits an ADMIN endpoint. 403, not 401 - we know who she is, she may not."
+show "$BASE/api/admin/stats" -H "Authorization: Bearer $ALICE"
+
+step "9. Same request with a scope-based rule (@PreAuthorize). Also 403."
+show "$BASE/api/reports" -H "Authorization: Bearer $ALICE"
+
+step "10. Login as root and repeat. 200."
+show -X POST "$BASE/api/auth/login" -H 'Content-Type: application/json' \
+     -d '{"username":"root","password":"root-password"}'
+ROOT=$(python3 -c "import json;print(json.load(open('/tmp/.b'))['accessToken'])")
+show "$BASE/api/admin/stats" -H "Authorization: Bearer $ROOT"
+
+step "11. Tampered payload, original signature. 401 invalid_token."
+HDR=$(echo "$ALICE" | cut -d. -f1); SIG=$(echo "$ALICE" | cut -d. -f3)
+FORGED_PAYLOAD=$(echo "$ALICE" | cut -d. -f2 | tr '_-' '/+' | sed 's/$/==/' | base64 -d 2>/dev/null \
+  | sed 's/"roles":\["USER"\]/"roles":["ADMIN"]/' | base64 -w0 | tr '/+' '_-' | tr -d '=')
+show "$BASE/api/admin/stats" -H "Authorization: Bearer $HDR.$FORGED_PAYLOAD.$SIG"
+
+step "12. Garbage where a token should be. 401, and note it is NOT 400."
+show "$BASE/api/me" -H "Authorization: Bearer not-a-jwt"
+
+step "13. Authorization header with no Bearer scheme. The resolver sees no token at all,\n#    so this is an authorization failure, not a token failure - note the bare realm."
+show "$BASE/api/me" -H "Authorization: $ALICE"
+
+step "14. A refresh token presented as an access token. 401 - the token_type claim."
+show "$BASE/api/me" -H "Authorization: Bearer $ALICE_REFRESH"
+
+step "15. Refresh with rotation. New access token, new refresh token."
+show -X POST "$BASE/api/auth/refresh" -H 'Content-Type: application/json' \
+     -d "{\"refreshToken\":\"$ALICE_REFRESH\"}"
+ALICE2=$(python3 -c "import json;print(json.load(open('/tmp/.b'))['accessToken'])")
+
+step "16. Replay the spent refresh token. 401 - rotation makes replay detectable."
+show -X POST "$BASE/api/auth/refresh" -H 'Content-Type: application/json' \
+     -d "{\"refreshToken\":\"$ALICE_REFRESH\"}"
+
+step "17. Logout revokes the presented access token by its jti."
+show -X POST "$BASE/api/auth/logout" -H "Authorization: Bearer $ALICE2"
+show "$BASE/api/auth/revocations" -H "Authorization: Bearer $ROOT"
+
+step "18. The revoked token, still cryptographically valid, is now refused."
+show "$BASE/api/me" -H "Authorization: Bearer $ALICE2"
+
+step "19. The real filter order, read from FilterChainProxy at runtime."
+show "$BASE/api/public/filters"
+
+step "20. SecurityContext across a thread boundary."
+show "$BASE/api/async-demo" -H "Authorization: Bearer $ROOT"
+
+hr
+echo "# end of transcript"
--- a/jwt-authentication/scripts/expiry-demo.sh
+++ b/jwt-authentication/scripts/expiry-demo.sh
@@ -0,0 +1,32 @@
+#!/usr/bin/env bash
+# Requires: --spring.profiles.active=hs256,shortlived  (2-second access tokens)
+set -u
+BASE="${1:-http://localhost:8080}"
+show() {
+  local out; out=$(curl -sS -D /tmp/.h -o /tmp/.b -w '%{http_code}' "$@")
+  printf 'HTTP %s\n' "$out"
+  grep -iE '^www-authenticate:' /tmp/.h | sed 's/\r$//'
+  [ -s /tmp/.b ] && { python3 -m json.tool < /tmp/.b 2>/dev/null | head -6 || cat /tmp/.b; }
+  echo
+}
+hr(){ printf '\n%s\n' "--------------------------------------------------------------------------"; }
+
+echo "=========================================================================="
+echo " jwt-auth-demo - token expiry and the 60-second clock skew"
+echo " profiles: hs256,shortlived   (access-token-ttl = 2s)"
+echo "=========================================================================="
+
+TOK=$(curl -sS -X POST "$BASE/api/auth/login" -H 'Content-Type: application/json' \
+      -d '{"username":"alice","password":"alice-password"}' | python3 -c 'import json,sys;print(json.load(sys.stdin)["accessToken"])')
+
+hr; echo "# T+0s  - fresh token"; echo; show "$BASE/api/me" -H "Authorization: Bearer $TOK"
+
+hr; echo "# T+5s  - exp has passed, but JwtTimestampValidator allows 60s of clock skew"
+echo "#         by default, so the token is STILL accepted. This surprises people"
+echo "#         who write a test that sleeps past exp and expects a 401."
+echo; sleep 5; show "$BASE/api/me" -H "Authorization: Bearer $TOK"
+
+hr; echo "# T+65s - past exp + the 60s skew window. Now it is refused."
+echo; sleep 60; show "$BASE/api/me" -H "Authorization: Bearer $TOK"
+
+hr; echo "# end"
--- a/jwt-authentication/scripts/resource-server-demo.sh
+++ b/jwt-authentication/scripts/resource-server-demo.sh
@@ -0,0 +1,38 @@
+#!/usr/bin/env bash
+# Compares the built-in resource server with and without a token_type validator.
+# Requires two runs; see docs/09-manual-filter-vs-resource-server.md
+set -u
+BASE="${1:-http://localhost:8080}"
+LABEL="${2:-resourceserver}"
+show() {
+  local out; out=$(curl -sS -D /tmp/.h -o /tmp/.b -w '%{http_code}' "$@")
+  printf 'HTTP %s\n' "$out"
+  grep -iE '^www-authenticate:' /tmp/.h | sed 's/\r$//'
+  [ -s /tmp/.b ] && { python3 -m json.tool < /tmp/.b 2>/dev/null | head -10 || cat /tmp/.b; echo; }
+}
+hr(){ printf '\n%s\n' "--------------------------------------------------------------------------"; }
+
+echo "=========================================================================="
+echo " jwt-auth-demo - built-in resource server"
+echo " profiles: $LABEL"
+echo "=========================================================================="
+
+R=$(curl -sS -X POST "$BASE/api/auth/login" -H 'Content-Type: application/json' \
+    -d '{"username":"alice","password":"alice-password"}')
+ACCESS=$(echo "$R" | python3 -c 'import json,sys;print(json.load(sys.stdin)["accessToken"])')
+REFRESH=$(echo "$R" | python3 -c 'import json,sys;print(json.load(sys.stdin)["refreshToken"])')
+
+hr; echo "# 1. The filter chain. Note BearerTokenAuthenticationFilter in place of our"
+echo "#    hand-written JwtAuthenticationFilter - same slot, framework-owned."
+echo; show "$BASE/api/public/filters"
+
+hr; echo "# 2. Access token -> 200."; echo; show "$BASE/api/me" -H "Authorization: Bearer $ACCESS"
+
+hr; echo "# 3. Non-admin on an admin route -> 403 insufficient_scope."
+echo; show "$BASE/api/admin/stats" -H "Authorization: Bearer $ACCESS"
+
+hr; echo "# 4. REFRESH token presented as an access token."
+echo "#    This is the line to watch when comparing the two runs."
+echo; show "$BASE/api/me" -H "Authorization: Bearer $REFRESH"
+
+hr; echo "# end"
--- a/jwt-authentication/scripts/rs256-demo.sh
+++ b/jwt-authentication/scripts/rs256-demo.sh
@@ -0,0 +1,45 @@
+#!/usr/bin/env bash
+# Requires: --spring.profiles.active=rs256
+set -u
+BASE="${1:-http://localhost:8080}"
+show() {
+  local out; out=$(curl -sS -D /tmp/.h -o /tmp/.b -w '%{http_code}' "$@")
+  printf 'HTTP %s\n' "$out"
+  grep -iE '^www-authenticate:' /tmp/.h | sed 's/\r$//'
+  [ -s /tmp/.b ] && { python3 -m json.tool < /tmp/.b 2>/dev/null || cat /tmp/.b; echo; }
+}
+jwt_part(){ echo "$1" | cut -d. -f$(( $2 + 1 )) | tr '_-' '/+' | sed 's/$/==/' | base64 -d 2>/dev/null | python3 -m json.tool 2>/dev/null; }
+hr(){ printf '\n%s\n' "--------------------------------------------------------------------------"; }
+
+echo "=========================================================================="
+echo " jwt-auth-demo - RS256 variant"
+echo " profiles: rs256   (private key signs, public key / JWKS verifies)"
+echo "=========================================================================="
+
+hr; echo "# 1. The public half, published as a JWK Set. No private material here -"
+echo "#    n and e only. Any number of resource servers can poll this."
+echo; show "$BASE/.well-known/jwks.json"
+
+hr; echo "# 2. Login. Same endpoint, same request, different signature algorithm."
+echo; show -X POST "$BASE/api/auth/login" -H 'Content-Type: application/json' \
+     -d '{"username":"root","password":"root-password"}'
+TOK=$(python3 -c "import json;print(json.load(open('/tmp/.b'))['accessToken'])")
+
+hr; echo "# 3. The JOSE header now carries alg=RS256 and the kid that selects the key."
+echo; jwt_part "$TOK" 0
+
+hr; echo "# 4. Token length. RS256 signatures are 256 bytes; HS256 signatures are 32."
+echo
+printf '  RS256 access token: %s characters\n' "${#TOK}"
+printf '  signature segment : %s characters\n' "$(echo "$TOK" | cut -d. -f3 | wc -c)"
+
+hr; echo "# 5. It works exactly the same from the caller's side."
+echo; show "$BASE/api/me" -H "Authorization: Bearer $TOK"
+
+hr; echo "# 6. Tampered payload, original signature -> 401, same as HS256."
+HDR=$(echo "$TOK" | cut -d. -f1); SIG=$(echo "$TOK" | cut -d. -f3)
+FORGED=$(echo "$TOK" | cut -d. -f2 | tr '_-' '/+' | sed 's/$/==/' | base64 -d 2>/dev/null \
+  | sed 's/"sub":"root"/"sub":"mallory"/' | base64 -w0 | tr '/+' '_-' | tr -d '=')
+echo; show "$BASE/api/me" -H "Authorization: Bearer $HDR.$FORGED.$SIG"
+
+hr; echo "# end"
--- a/jwt-authentication/scripts/run-all.sh
+++ b/jwt-authentication/scripts/run-all.sh
@@ -0,0 +1,42 @@
+#!/usr/bin/env bash
+# Regenerates every file under ../docs/output/ from a real run.
+# Usage: ./scripts/run-all.sh
+set -eu
+cd "$(dirname "$0")/.."
+
+echo "==> mvn test"
+{
+  echo "=========================================================================="
+  echo " jwt-auth-demo - test run"
+  echo "=========================================================================="
+  echo
+  mvn -B test 2>&1 | grep -E '^\[INFO\] (Running|Tests run)|^\[ERROR\]|BUILD (SUCCESS|FAILURE)' \
+    | sed 's/^\[INFO\] //'
+  echo
+  echo "JDK      : $(java -version 2>&1 | grep -v JAVA_TOOL | head -1)"
+  echo "Boot     : 4.1.1"
+  echo "Security : 7.1.1"
+} > ../docs/output/test-run.txt
+
+echo "==> hs256 (manual filter) transcript"
+./scripts/run.sh hs256           >/dev/null && ./scripts/curl-transcript.sh > ../docs/output/curl-transcript-hs256.txt 2>&1
+
+echo "==> rs256 transcript"
+./scripts/run.sh rs256           >/dev/null && ./scripts/rs256-demo.sh      > ../docs/output/rs256-demo.txt 2>&1
+
+echo "==> csrf vs permitAll"
+./scripts/run.sh hs256,csrfon    >/dev/null && ./scripts/csrf-demo.sh       > ../docs/output/csrf-vs-permitall.txt 2>&1
+
+echo "==> expiry and clock skew (takes ~70s)"
+./scripts/run.sh hs256,shortlived >/dev/null && ./scripts/expiry-demo.sh    > ../docs/output/expiry-and-clock-skew.txt 2>&1
+
+echo "==> built-in resource server, without and with the token_type validator"
+./scripts/run.sh hs256,resourceserver >/dev/null \
+  && ./scripts/resource-server-demo.sh http://localhost:8080 "hs256,resourceserver" \
+     > ../docs/output/resource-server-loose.txt 2>&1
+./scripts/run.sh hs256,resourceserver,strict >/dev/null \
+  && ./scripts/resource-server-demo.sh http://localhost:8080 "hs256,resourceserver,strict" \
+     > ../docs/output/resource-server-strict.txt 2>&1
+
+for p in $(ps -eo pid,cmd | grep '[J]wtAuthDemoApplication' | awk '{print $1}'); do kill -9 "$p" || true; done
+echo "==> done. docs/output/ regenerated."
--- a/jwt-authentication/scripts/run.sh
+++ b/jwt-authentication/scripts/run.sh
@@ -0,0 +1,16 @@
+#!/usr/bin/env bash
+# Starts the app on a clean port 8080 with the given profiles.
+# Usage: ./scripts/run.sh [profiles]   e.g. ./scripts/run.sh rs256,resourceserver
+set -eu
+PROFILES="${1:-hs256}"
+for p in $(ps -eo pid,cmd | grep '[J]wtAuthDemoApplication' | awk '{print $1}'); do kill -9 "$p" || true; done
+sleep 2
+setsid nohup mvn -B -o org.springframework.boot:spring-boot-maven-plugin:run \
+  -Dspring-boot.run.profiles="$PROFILES" > "/tmp/app-${PROFILES//,/-}.log" 2>&1 < /dev/null &
+for i in $(seq 1 60); do
+  if curl -s -o /dev/null http://localhost:8080/api/public/ping 2>/dev/null; then
+    echo "started with profiles: $PROFILES"; exit 0
+  fi
+  sleep 2
+done
+echo "failed to start; see /tmp/app-${PROFILES//,/-}.log" >&2; exit 1
--- a/jwt-authentication/src/main/java/com/ankurm/jwtauth/JwtAuthDemoApplication.java
+++ b/jwt-authentication/src/main/java/com/ankurm/jwtauth/JwtAuthDemoApplication.java
@@ -0,0 +1,31 @@
+package com.ankurm.jwtauth;
+
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+
+/**
+ * Runnable companion for the ankurm.com article
+ * "Spring Security 7.1 JWT Authentication: The Complete Guide (Spring Boot 4.1)".
+ *
+ * <p>Two signing variants are wired as Spring profiles:
+ * <ul>
+ *   <li>{@code hs256} (default) - symmetric HMAC, one shared secret.</li>
+ *   <li>{@code rs256} - asymmetric RSA, private key signs, public key (JWKS) verifies.</li>
+ * </ul>
+ *
+ * <p>Two validation styles are wired as Spring profiles too:
+ * <ul>
+ *   <li>{@code manual} (default) - a hand-written {@code OncePerRequestFilter}.</li>
+ *   <li>{@code resourceserver} - Spring Security's built-in
+ *       {@code oauth2ResourceServer().jwt()} support.</li>
+ * </ul>
+ *
+ * @see docs/01-architecture.md
+ */
+@SpringBootApplication
+public class JwtAuthDemoApplication {
+
+    public static void main(String[] args) {
+        SpringApplication.run(JwtAuthDemoApplication.class, args);
+    }
+}
--- a/jwt-authentication/src/main/java/com/ankurm/jwtauth/auth/AuthController.java
+++ b/jwt-authentication/src/main/java/com/ankurm/jwtauth/auth/AuthController.java
@@ -0,0 +1,121 @@
+package com.ankurm.jwtauth.auth;
+
+import jakarta.validation.Valid;
+import org.springframework.http.ResponseEntity;
+import org.springframework.security.authentication.AuthenticationManager;
+import org.springframework.security.authentication.BadCredentialsException;
+import org.springframework.security.authentication.UsernamePasswordAuthenticationToken;
+import org.springframework.security.core.Authentication;
+import org.springframework.security.core.AuthenticationException;
+import org.springframework.security.core.userdetails.UserDetails;
+import org.springframework.security.core.userdetails.UserDetailsService;
+import org.springframework.security.oauth2.jwt.Jwt;
+import org.springframework.security.oauth2.jwt.JwtDecoder;
+import org.springframework.security.oauth2.jwt.JwtException;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.PostMapping;
+import org.springframework.web.bind.annotation.RequestBody;
+import org.springframework.web.bind.annotation.RequestMapping;
+import org.springframework.web.bind.annotation.RestController;
+
+import com.ankurm.jwtauth.auth.AuthDtos.LoginRequest;
+import com.ankurm.jwtauth.auth.AuthDtos.RefreshRequest;
+import com.ankurm.jwtauth.auth.AuthDtos.TokenResponse;
+
+/**
+ * The login endpoint. It is the only place that sees a password, and the only
+ * place that calls the {@code AuthenticationManager}.
+ *
+ * <p>Everything after this point in the system is stateless: no session is created,
+ * and the {@code SecurityContext} written here is deliberately NOT persisted.
+ */
+@RestController
+@RequestMapping("/api/auth")
+public class AuthController {
+
+    private final AuthenticationManager authenticationManager;
+    private final TokenService tokenService;
+    private final JwtDecoder jwtDecoder;
+    private final UserDetailsService userDetailsService;
+    private final RevokedTokenStore revokedTokens;
+
+    public AuthController(AuthenticationManager authenticationManager,
+                          TokenService tokenService,
+                          JwtDecoder jwtDecoder,
+                          UserDetailsService userDetailsService,
+                          RevokedTokenStore revokedTokens) {
+        this.authenticationManager = authenticationManager;
+        this.tokenService = tokenService;
+        this.jwtDecoder = jwtDecoder;
+        this.userDetailsService = userDetailsService;
+        this.revokedTokens = revokedTokens;
+    }
+
+    @PostMapping("/login")
+    public TokenResponse login(@Valid @RequestBody LoginRequest request) {
+        // Throws BadCredentialsException / LockedException / DisabledException,
+        // all AuthenticationException subtypes -> 401 via the exception handler.
+        Authentication authentication = this.authenticationManager.authenticate(
+                UsernamePasswordAuthenticationToken.unauthenticated(
+                        request.username(), request.password()));
+
+        TokenService.IssuedToken access = this.tokenService.issueAccessToken(authentication);
+        TokenService.IssuedToken refresh = this.tokenService.issueRefreshToken(authentication.getName());
+
+        return new TokenResponse(access.value(), refresh.value(), "Bearer", access.expiresInSeconds());
+    }
+
+    /**
+     * Refresh with rotation: the presented refresh token is revoked as it is spent.
+     * Replaying it is then a detectable event, not a silent success.
+     */
+    @PostMapping("/refresh")
+    public TokenResponse refresh(@Valid @RequestBody RefreshRequest request) {
+        Jwt jwt;
+        try {
+            jwt = this.jwtDecoder.decode(request.refreshToken());
+        }
+        catch (JwtException ex) {
+            throw new BadCredentialsException("Refresh token is not valid", ex);
+        }
+
+        if (!TokenService.REFRESH.equals(jwt.getClaimAsString("token_type"))) {
+            throw new BadCredentialsException("Not a refresh token");
+        }
+        if (this.revokedTokens.isRevoked(jwt.getId())) {
+            throw new BadCredentialsException("Refresh token already used or revoked");
+        }
+        this.revokedTokens.revoke(jwt.getId(), jwt.getExpiresAt());
+
+        UserDetails user = this.userDetailsService.loadUserByUsername(jwt.getSubject());
+        Authentication authentication = UsernamePasswordAuthenticationToken.authenticated(
+                user, null, user.getAuthorities());
+
+        TokenService.IssuedToken access = this.tokenService.issueAccessToken(authentication);
+        TokenService.IssuedToken newRefresh = this.tokenService.issueRefreshToken(user.getUsername());
+
+        return new TokenResponse(access.value(), newRefresh.value(), "Bearer", access.expiresInSeconds());
+    }
+
+    /** Revokes the presented access token by jti. Requires a valid token to call. */
+    @PostMapping("/logout")
+    public ResponseEntity<Void> logout(Authentication authentication) {
+        if (authentication instanceof
+                org.springframework.security.oauth2.server.resource.authentication.JwtAuthenticationToken jwtAuth) {
+            Jwt jwt = jwtAuth.getToken();
+            this.revokedTokens.revoke(jwt.getId(), jwt.getExpiresAt());
+        }
+        return ResponseEntity.noContent().build();
+    }
+
+    @GetMapping("/revocations")
+    public java.util.Map<String, Integer> revocations() {
+        return java.util.Map.of("revokedTokens", this.revokedTokens.size());
+    }
+
+    static class LoginFailed extends RuntimeException {
+        LoginFailed(AuthenticationException cause) {
+            super(cause);
+        }
+    }
+}
--- a/jwt-authentication/src/main/java/com/ankurm/jwtauth/auth/AuthDtos.java
+++ b/jwt-authentication/src/main/java/com/ankurm/jwtauth/auth/AuthDtos.java
@@ -0,0 +1,17 @@
+package com.ankurm.jwtauth.auth;
+
+import jakarta.validation.constraints.NotBlank;
+
+public final class AuthDtos {
+
+    private AuthDtos() { }
+
+    public record LoginRequest(@NotBlank String username, @NotBlank String password) { }
+
+    public record RefreshRequest(@NotBlank String refreshToken) { }
+
+    public record TokenResponse(String accessToken,
+                                String refreshToken,
+                                String tokenType,
+                                long expiresIn) { }
+}
--- a/jwt-authentication/src/main/java/com/ankurm/jwtauth/auth/JwtAuthenticationFilter.java
+++ b/jwt-authentication/src/main/java/com/ankurm/jwtauth/auth/JwtAuthenticationFilter.java
@@ -0,0 +1,178 @@
+package com.ankurm.jwtauth.auth;
+
+import java.io.IOException;
+import java.util.List;
+
+import jakarta.servlet.FilterChain;
+import jakarta.servlet.ServletException;
+import jakarta.servlet.http.HttpServletRequest;
+import jakarta.servlet.http.HttpServletResponse;
+import org.springframework.security.oauth2.server.resource.InvalidBearerTokenException;
+import org.springframework.security.core.GrantedAuthority;
+import org.springframework.security.core.context.SecurityContext;
+import org.springframework.security.core.context.SecurityContextHolder;
+import org.springframework.security.core.context.SecurityContextHolderStrategy;
+import org.springframework.security.oauth2.core.OAuth2AuthenticationException;
+import org.springframework.security.oauth2.core.OAuth2Error;
+import org.springframework.security.oauth2.jwt.Jwt;
+import org.springframework.security.oauth2.jwt.JwtDecoder;
+import org.springframework.security.oauth2.jwt.JwtException;
+import org.springframework.security.oauth2.server.resource.BearerTokenErrorCodes;
+import org.springframework.security.oauth2.server.resource.authentication.JwtAuthenticationConverter;
+import org.springframework.security.oauth2.server.resource.web.BearerTokenResolver;
+import org.springframework.security.oauth2.server.resource.web.DefaultBearerTokenResolver;
+import org.springframework.security.web.AuthenticationEntryPoint;
+import org.springframework.security.web.context.RequestAttributeSecurityContextRepository;
+import org.springframework.security.web.context.SecurityContextRepository;
+import org.springframework.web.filter.OncePerRequestFilter;
+
+/**
+ * The hand-written half of the flow: read the bearer token, verify it, put an
+ * {@code Authentication} in the {@code SecurityContext}, continue the chain.
+ *
+ * <p>Five details separate a filter that works from one that only appears to:
+ * <ol>
+ *   <li>It extends {@link OncePerRequestFilter}, so a {@code FORWARD} to an error
+ *       page or a {@code @Async} dispatch does not run authentication twice.</li>
+ *   <li>No token present is <em>not</em> an error. The filter continues the chain and
+ *       lets {@code AuthorizationFilter} decide - that is what makes {@code permitAll()}
+ *       endpoints reachable without a token.</li>
+ *   <li>A token that <em>is</em> present but bad is an error, and the chain stops. The
+ *       alternative - continuing anonymously - turns a forged token into a 403 on a
+ *       protected endpoint and a silent 200 on a public one.</li>
+ *   <li>The context is written through {@link SecurityContextHolderStrategy}, not the
+ *       static {@code SecurityContextHolder} setters, and also saved into the
+ *       {@link SecurityContextRepository} so it survives a dispatch.</li>
+ *   <li>The context is cleared on failure, so a pooled thread cannot leak a previous
+ *       request's principal.</li>
+ * </ol>
+ *
+ * @see docs/02-filter-chain-and-ordering.md
+ */
+public class JwtAuthenticationFilter extends OncePerRequestFilter {
+
+    private final JwtDecoder jwtDecoder;
+    private final RevokedTokenStore revokedTokens;
+    private final AuthenticationEntryPoint entryPoint;
+
+    private final BearerTokenResolver bearerTokenResolver = new DefaultBearerTokenResolver();
+    private final JwtAuthenticationConverter authenticationConverter = defaultConverter();
+    private final SecurityContextHolderStrategy contextHolderStrategy =
+            SecurityContextHolder.getContextHolderStrategy();
+    private final SecurityContextRepository contextRepository =
+            new RequestAttributeSecurityContextRepository();
+
+    public JwtAuthenticationFilter(JwtDecoder jwtDecoder,
+                                   RevokedTokenStore revokedTokens,
+                                   AuthenticationEntryPoint entryPoint) {
+        this.jwtDecoder = jwtDecoder;
+        this.revokedTokens = revokedTokens;
+        this.entryPoint = entryPoint;
+    }
+
+    @Override
+    protected void doFilterInternal(HttpServletRequest request,
+                                    HttpServletResponse response,
+                                    FilterChain filterChain) throws ServletException, IOException {
+
+        String token;
+        try {
+            token = this.bearerTokenResolver.resolve(request);
+        }
+        catch (OAuth2AuthenticationException ex) {
+            // Malformed Authorization header, or a token in two places at once.
+            this.contextHolderStrategy.clearContext();
+            this.entryPoint.commence(request, response, ex);
+            return;
+        }
+
+        if (token == null) {
+            // (2) No credentials offered. Not our business - let authorization decide.
+            filterChain.doFilter(request, response);
+            return;
+        }
+
+        try {
+            Jwt jwt = this.jwtDecoder.decode(token);
+            assertIsAccessToken(jwt);
+            assertNotRevoked(jwt);
+
+            SecurityContext context = this.contextHolderStrategy.createEmptyContext();
+            context.setAuthentication(this.authenticationConverter.convert(jwt));
+            this.contextHolderStrategy.setContext(context);
+            this.contextRepository.saveContext(context, request, response);
+        }
+        catch (JwtException | OAuth2AuthenticationException ex) {
+            // (3) and (5): stop the chain, clear the context, answer 401.
+            this.contextHolderStrategy.clearContext();
+            this.entryPoint.commence(request, response, asAuthenticationException(ex));
+            return;
+        }
+
+        filterChain.doFilter(request, response);
+    }
+
+    private void assertIsAccessToken(Jwt jwt) {
+        if (!TokenService.ACCESS.equals(jwt.getClaimAsString("token_type"))) {
+            throw invalidToken("This endpoint accepts access tokens only");
+        }
+    }
+
+    private void assertNotRevoked(Jwt jwt) {
+        if (this.revokedTokens.isRevoked(jwt.getId())) {
+            throw invalidToken("Token has been revoked");
+        }
+    }
+
+    private static OAuth2AuthenticationException invalidToken(String description) {
+        OAuth2Error error = new OAuth2Error(
+                BearerTokenErrorCodes.INVALID_TOKEN,
+                description,
+                "https://tools.ietf.org/html/rfc6750#section-3.1");
+        return new OAuth2AuthenticationException(error, description);
+    }
+
+    /**
+     * Detail that decides what the client sees. {@code BearerTokenAuthenticationEntryPoint}
+     * only writes {@code error="invalid_token"} into WWW-Authenticate when the exception
+     * carries a {@code BearerTokenError}. Wrap a {@code JwtException} in a plain
+     * {@code AuthenticationServiceException} and the client gets a bare
+     * {@code WWW-Authenticate: Bearer realm="..."} with no reason at all.
+     */
+    private static org.springframework.security.core.AuthenticationException asAuthenticationException(
+            Exception ex) {
+        if (ex instanceof org.springframework.security.core.AuthenticationException authEx) {
+            return authEx;
+        }
+        return new InvalidBearerTokenException(ex.getMessage(), ex);
+    }
+
+    private static JwtAuthenticationConverter defaultConverter() {
+        JwtAuthenticationConverter converter = new JwtAuthenticationConverter();
+        converter.setJwtGrantedAuthoritiesConverter(JwtAuthenticationFilter::authorities);
+        return converter;
+    }
+
+    /**
+     * "scope" -> SCOPE_x (Spring's default) plus "roles" -> ROLE_x, so
+     * {@code hasRole("ADMIN")} and {@code hasAuthority("SCOPE_admin:read")} both work.
+     */
+    private static List<GrantedAuthority> authorities(Jwt jwt) {
+        List<GrantedAuthority> result = new java.util.ArrayList<>();
+        String scope = jwt.getClaimAsString("scope");
+        if (scope != null && !scope.isBlank()) {
+            for (String s : scope.split("\\s+")) {
+                result.add(new org.springframework.security.core.authority.SimpleGrantedAuthority(
+                        "SCOPE_" + s));
+            }
+        }
+        List<String> roles = jwt.getClaimAsStringList("roles");
+        if (roles != null) {
+            for (String role : roles) {
+                result.add(new org.springframework.security.core.authority.SimpleGrantedAuthority(
+                        "ROLE_" + role));
+            }
+        }
+        return result;
+    }
+}
--- a/jwt-authentication/src/main/java/com/ankurm/jwtauth/auth/RevokedTokenStore.java
+++ b/jwt-authentication/src/main/java/com/ankurm/jwtauth/auth/RevokedTokenStore.java
@@ -0,0 +1,40 @@
+package com.ankurm.jwtauth.auth;
+
+import java.time.Instant;
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+
+import org.springframework.stereotype.Component;
+
+/**
+ * The smallest thing that makes a stateless token revocable: a jti denylist.
+ *
+ * <p>Entries only need to outlive the token's own expiry, so the map self-prunes.
+ * In production this is Redis with a TTL, not a map - but the shape is identical.
+ * See docs/07-edge-cases.md#logout-and-revocation.
+ */
+@Component
+public class RevokedTokenStore {
+
+    private final Map<String, Instant> revoked = new ConcurrentHashMap<>();
+
+    public void revoke(String jti, Instant expiresAt) {
+        prune();
+        this.revoked.put(jti, expiresAt);
+    }
+
+    public boolean isRevoked(String jti) {
+        prune();
+        return jti != null && this.revoked.containsKey(jti);
+    }
+
+    public int size() {
+        prune();
+        return this.revoked.size();
+    }
+
+    private void prune() {
+        Instant now = Instant.now();
+        this.revoked.entrySet().removeIf(e -> e.getValue() != null && e.getValue().isBefore(now));
+    }
+}
--- a/jwt-authentication/src/main/java/com/ankurm/jwtauth/auth/TokenService.java
+++ b/jwt-authentication/src/main/java/com/ankurm/jwtauth/auth/TokenService.java
@@ -0,0 +1,112 @@
+package com.ankurm.jwtauth.auth;
+
+import java.time.Duration;
+import java.time.Instant;
+import java.util.List;
+import java.util.UUID;
+import java.util.stream.Collectors;
+
+import org.springframework.beans.factory.annotation.Value;
+import org.springframework.security.core.Authentication;
+import org.springframework.security.core.GrantedAuthority;
+import org.springframework.security.oauth2.jwt.JwsHeader;
+import org.springframework.security.oauth2.jwt.Jwt;
+import org.springframework.security.oauth2.jwt.JwtClaimsSet;
+import org.springframework.security.oauth2.jwt.JwtEncoder;
+import org.springframework.security.oauth2.jwt.JwtEncoderParameters;
+import org.springframework.stereotype.Service;
+
+/**
+ * Mints the tokens. This is the "token issue" step of the flow.
+ *
+ * <p>Two claims here are not decoration:
+ * <ul>
+ *   <li>{@code token_type} - separates access tokens from refresh tokens. Without it,
+ *       a refresh token is a perfectly valid access token, because both are signed
+ *       by the same key. See docs/07-edge-cases.md#refresh-token-as-access-token.</li>
+ *   <li>{@code jti} - a per-token id, which is what a denylist keys on. A JWT is not
+ *       revocable without one.</li>
+ * </ul>
+ */
+@Service
+public class TokenService {
+
+    public static final String ACCESS = "access";
+    public static final String REFRESH = "refresh";
+
+    private final JwtEncoder encoder;
+    private final String issuer;
+    private final String audience;
+    private final Duration accessTtl;
+    private final Duration refreshTtl;
+
+    public TokenService(JwtEncoder encoder,
+                        @Value("${demo.jwt.issuer}") String issuer,
+                        @Value("${demo.jwt.audience}") String audience,
+                        @Value("${demo.jwt.access-token-ttl}") Duration accessTtl,
+                        @Value("${demo.jwt.refresh-token-ttl}") Duration refreshTtl) {
+        this.encoder = encoder;
+        this.issuer = issuer;
+        this.audience = audience;
+        this.accessTtl = accessTtl;
+        this.refreshTtl = refreshTtl;
+    }
+
+    public IssuedToken issueAccessToken(Authentication authentication) {
+        List<String> authorities = authentication.getAuthorities().stream()
+                .map(GrantedAuthority::getAuthority)
+                .sorted()
+                .toList();
+
+        // Spring Security's default JwtGrantedAuthoritiesConverter reads the "scope"
+        // claim and prefixes each value with SCOPE_. We keep roles in a separate
+        // "roles" claim so the two authority families stay distinguishable.
+        String scope = authorities.stream()
+                .filter(a -> a.startsWith("SCOPE_"))
+                .map(a -> a.substring("SCOPE_".length()))
+                .collect(Collectors.joining(" "));
+        List<String> roles = authorities.stream()
+                .filter(a -> a.startsWith("ROLE_"))
+                .map(a -> a.substring("ROLE_".length()))
+                .toList();
+
+        return encode(authentication.getName(), ACCESS, this.accessTtl, claims -> claims
+                .claim("scope", scope)
+                .claim("roles", roles));
+    }
+
+    public IssuedToken issueRefreshToken(String subject) {
+        return encode(subject, REFRESH, this.refreshTtl, claims -> { });
+    }
+
+    private IssuedToken encode(String subject, String tokenType, Duration ttl,
+                               java.util.function.Consumer<JwtClaimsSet.Builder> extra) {
+        Instant now = Instant.now();
+        String jti = UUID.randomUUID().toString();
+
+        JwtClaimsSet.Builder claims = JwtClaimsSet.builder()
+                .issuer(this.issuer)
+                .audience(List.of(this.audience))
+                .subject(subject)
+                .id(jti)                       // -> "jti"
+                .issuedAt(now)                 // -> "iat"
+                .notBefore(now)                // -> "nbf"
+                .expiresAt(now.plus(ttl))      // -> "exp"
+                .claim("token_type", tokenType);
+        extra.accept(claims);
+
+        // Passing JwsHeader explicitly is optional - the encoder derives the algorithm
+        // from the key - but being explicit documents intent and fails loudly on a
+        // key/algorithm mismatch.
+        Jwt jwt = this.encoder.encode(JwtEncoderParameters.from(claims.build()));
+        return new IssuedToken(jwt.getTokenValue(), jti, jwt.getExpiresAt(), ttl.toSeconds());
+    }
+
+    /** Unused overload kept to show the explicit-header form. */
+    @SuppressWarnings("unused")
+    private Jwt encodeWithExplicitHeader(JwsHeader header, JwtClaimsSet claims) {
+        return this.encoder.encode(JwtEncoderParameters.from(header, claims));
+    }
+
+    public record IssuedToken(String value, String jti, Instant expiresAt, long expiresInSeconds) { }
+}
--- a/jwt-authentication/src/main/java/com/ankurm/jwtauth/config/ApiExceptionHandler.java
+++ b/jwt-authentication/src/main/java/com/ankurm/jwtauth/config/ApiExceptionHandler.java
@@ -0,0 +1,41 @@
+package com.ankurm.jwtauth.config;
+
+import java.net.URI;
+
+import org.springframework.http.HttpStatus;
+import org.springframework.http.ProblemDetail;
+import org.springframework.security.authentication.BadCredentialsException;
+import org.springframework.security.authentication.DisabledException;
+import org.springframework.security.authentication.LockedException;
+import org.springframework.security.core.AuthenticationException;
+import org.springframework.web.bind.annotation.ExceptionHandler;
+import org.springframework.web.bind.annotation.RestControllerAdvice;
+
+/**
+ * Login failures arrive here, not at the {@code AuthenticationEntryPoint} - the
+ * controller calls {@code AuthenticationManager} itself, so the exception is a plain
+ * MVC exception by the time anything security-shaped could see it.
+ *
+ * <p>Note every branch answers 401 with the same body. Telling a caller that the
+ * username exists but the password is wrong is a user-enumeration oracle.
+ */
+@RestControllerAdvice
+public class ApiExceptionHandler {
+
+    @ExceptionHandler({BadCredentialsException.class, LockedException.class, DisabledException.class})
+    public ProblemDetail onAuthenticationFailure(AuthenticationException ex) {
+        ProblemDetail problem = ProblemDetail.forStatus(HttpStatus.UNAUTHORIZED);
+        problem.setType(URI.create("https://ankurm.com/problems/invalid-credentials"));
+        problem.setTitle("Authentication failed");
+        problem.setDetail("Invalid username or password");
+        return problem;
+    }
+
+    @ExceptionHandler(AuthenticationException.class)
+    public ProblemDetail onAuthentication(AuthenticationException ex) {
+        ProblemDetail problem = ProblemDetail.forStatus(HttpStatus.UNAUTHORIZED);
+        problem.setTitle("Authentication failed");
+        problem.setDetail("Invalid username or password");
+        return problem;
+    }
+}
--- a/jwt-authentication/src/main/java/com/ankurm/jwtauth/config/AppUsers.java
+++ b/jwt-authentication/src/main/java/com/ankurm/jwtauth/config/AppUsers.java
@@ -0,0 +1,46 @@
+package com.ankurm.jwtauth.config;
+
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.security.core.userdetails.User;
+import org.springframework.security.core.userdetails.UserDetails;
+import org.springframework.security.core.userdetails.UserDetailsService;
+import org.springframework.security.crypto.factory.PasswordEncoderFactories;
+import org.springframework.security.crypto.password.PasswordEncoder;
+import org.springframework.security.provisioning.InMemoryUserDetailsManager;
+
+/**
+ * Demo user store. In-memory on purpose: this repository is about the token
+ * pipeline, not about where users live.
+ *
+ * <p>Note there is deliberately NO {@code AuthenticationManager} bean exposed by
+ * auto-configuration once a {@code SecurityFilterChain} bean exists - we build one
+ * explicitly in {@link SecurityConfig} so the login endpoint can call it.
+ */
+@Configuration
+public class AppUsers {
+
+    @Bean
+    public PasswordEncoder passwordEncoder() {
+        // DelegatingPasswordEncoder: stores {bcrypt}$2a$... so the hash format is upgradable.
+        return PasswordEncoderFactories.createDelegatingPasswordEncoder();
+    }
+
+    @Bean
+    public UserDetailsService userDetailsService(PasswordEncoder encoder) {
+        UserDetails alice = User.withUsername("alice")
+                .password(encoder.encode("alice-password"))
+                .authorities("ROLE_USER", "SCOPE_profile:read")
+                .build();
+        UserDetails root = User.withUsername("root")
+                .password(encoder.encode("root-password"))
+                .authorities("ROLE_USER", "ROLE_ADMIN", "SCOPE_profile:read", "SCOPE_admin:read")
+                .build();
+        UserDetails locked = User.withUsername("locked")
+                .password(encoder.encode("locked-password"))
+                .authorities("ROLE_USER")
+                .accountLocked(true)
+                .build();
+        return new InMemoryUserDetailsManager(alice, root, locked);
+    }
+}
--- a/jwt-authentication/src/main/java/com/ankurm/jwtauth/config/Hs256KeyConfig.java
+++ b/jwt-authentication/src/main/java/com/ankurm/jwtauth/config/Hs256KeyConfig.java
@@ -0,0 +1,74 @@
+package com.ankurm.jwtauth.config;
+
+import javax.crypto.SecretKey;
+import javax.crypto.spec.SecretKeySpec;
+import java.nio.charset.StandardCharsets;
+
+import com.nimbusds.jose.jwk.source.ImmutableSecret;
+import com.nimbusds.jose.proc.SecurityContext;
+import org.springframework.beans.factory.ObjectProvider;
+import org.springframework.beans.factory.annotation.Value;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.context.annotation.Profile;
+import org.springframework.security.oauth2.jose.jws.MacAlgorithm;
+import org.springframework.security.oauth2.core.OAuth2TokenValidator;
+import org.springframework.security.oauth2.jwt.Jwt;
+import org.springframework.security.oauth2.jwt.JwtDecoder;
+import org.springframework.security.oauth2.jwt.JwtEncoder;
+import org.springframework.security.oauth2.jwt.NimbusJwtDecoder;
+import org.springframework.security.oauth2.jwt.NimbusJwtEncoder;
+
+/**
+ * HS256 variant: one symmetric secret both signs and verifies.
+ *
+ * <p>The secret must be at least 256 bits (32 bytes) for HS256 - Nimbus enforces
+ * this and throws {@code KeyLengthException} otherwise. See docs/05-hs256-vs-rs256.md.
+ */
+@Configuration
+@Profile("hs256")
+public class Hs256KeyConfig {
+
+    private final SecretKey secretKey;
+
+    private final String issuer;
+    private final String audience;
+
+    public Hs256KeyConfig(@Value("${demo.jwt.hmac-secret}") String secret,
+                          @Value("${demo.jwt.issuer}") String issuer,
+                          @Value("${demo.jwt.audience}") String audience) {
+        this.issuer = issuer;
+        this.audience = audience;
+        byte[] bytes = secret.getBytes(StandardCharsets.UTF_8);
+        if (bytes.length < 32) {
+            throw new IllegalStateException(
+                    "demo.jwt.hmac-secret must be >= 32 bytes for HS256, got " + bytes.length);
+        }
+        this.secretKey = new SecretKeySpec(bytes, "HmacSHA256");
+    }
+
+    @Bean
+    public JwtEncoder jwtEncoder() {
+        // Spring Security 7.0 added the withSecretKey builder; the older
+        // new NimbusJwtEncoder(new ImmutableSecret<>(key)) form still works.
+        return NimbusJwtEncoder.withSecretKey(this.secretKey)
+                .algorithm(MacAlgorithm.HS256)
+                .build();
+    }
+
+    @Bean
+    public JwtDecoder jwtDecoder(ObjectProvider<OAuth2TokenValidator<Jwt>> extraValidators) {
+        NimbusJwtDecoder decoder = NimbusJwtDecoder.withSecretKey(this.secretKey)
+                .macAlgorithm(MacAlgorithm.HS256)   // pin the algorithm - see docs/07-edge-cases.md
+                .build();
+        decoder.setJwtValidator(JwtValidatorFactory.compose(this.issuer, this.audience, extraValidators));
+        return decoder;
+    }
+
+    /** Kept only to show the pre-7.0 constructor still compiles. Not a bean. */
+    @SuppressWarnings("unused")
+    private JwtEncoder legacyStyleEncoder() {
+        ImmutableSecret<SecurityContext> jwkSource = new ImmutableSecret<>(this.secretKey);
+        return new NimbusJwtEncoder(jwkSource);
+    }
+}
--- a/jwt-authentication/src/main/java/com/ankurm/jwtauth/config/JwtValidatorFactory.java
+++ b/jwt-authentication/src/main/java/com/ankurm/jwtauth/config/JwtValidatorFactory.java
@@ -0,0 +1,37 @@
+package com.ankurm.jwtauth.config;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import com.ankurm.jwtauth.edge.AudienceValidator;
+import org.springframework.beans.factory.ObjectProvider;
+import org.springframework.security.oauth2.core.DelegatingOAuth2TokenValidator;
+import org.springframework.security.oauth2.core.OAuth2TokenValidator;
+import org.springframework.security.oauth2.jwt.Jwt;
+import org.springframework.security.oauth2.jwt.JwtValidators;
+
+/**
+ * Builds the validator stack applied to every decoded token.
+ *
+ * <p>What {@code JwtValidators.createDefaultWithIssuer(issuer)} gives you:
+ * {@code exp} and {@code nbf} (with 60 seconds of clock skew) plus {@code iss}.
+ * What it does NOT give you: {@code aud}. That one is added here explicitly,
+ * because a token minted for another service in the same estate is otherwise
+ * accepted without complaint.
+ *
+ * @see docs/07-edge-cases.md
+ */
+final class JwtValidatorFactory {
+
+    private JwtValidatorFactory() { }
+
+    static OAuth2TokenValidator<Jwt> compose(String issuer,
+                                             String audience,
+                                             ObjectProvider<OAuth2TokenValidator<Jwt>> extras) {
+        List<OAuth2TokenValidator<Jwt>> validators = new ArrayList<>();
+        validators.add(JwtValidators.createDefaultWithIssuer(issuer));  // exp, nbf, iss
+        validators.add(AudienceValidator.forAudience(audience));        // aud - not default
+        extras.orderedStream().forEach(validators::add);                // e.g. token_type
+        return new DelegatingOAuth2TokenValidator<>(validators);
+    }
+}
--- a/jwt-authentication/src/main/java/com/ankurm/jwtauth/config/ResourceServerSecurityConfig.java
+++ b/jwt-authentication/src/main/java/com/ankurm/jwtauth/config/ResourceServerSecurityConfig.java
@@ -0,0 +1,117 @@
+package com.ankurm.jwtauth.config;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.context.annotation.Profile;
+import org.springframework.core.convert.converter.Converter;
+import org.springframework.security.authentication.AbstractAuthenticationToken;
+import org.springframework.security.authentication.AuthenticationManager;
+import org.springframework.security.authentication.ProviderManager;
+import org.springframework.security.authentication.dao.DaoAuthenticationProvider;
+import org.springframework.security.config.annotation.method.configuration.EnableMethodSecurity;
+import org.springframework.security.config.annotation.web.builders.HttpSecurity;
+import org.springframework.security.config.annotation.web.configuration.EnableWebSecurity;
+import org.springframework.security.config.http.SessionCreationPolicy;
+import org.springframework.security.core.GrantedAuthority;
+import org.springframework.security.core.authority.SimpleGrantedAuthority;
+import org.springframework.security.core.userdetails.UserDetailsService;
+import org.springframework.security.crypto.password.PasswordEncoder;
+import org.springframework.security.oauth2.jwt.Jwt;
+import org.springframework.security.oauth2.server.resource.authentication.JwtAuthenticationConverter;
+import org.springframework.security.oauth2.server.resource.authentication.JwtGrantedAuthoritiesConverter;
+import org.springframework.security.web.SecurityFilterChain;
+import org.springframework.security.web.context.NullSecurityContextRepository;
+
+/**
+ * The same API secured by Spring Security's built-in resource server instead of a
+ * hand-written filter. Run with {@code --spring.profiles.active=hs256,resourceserver}.
+ *
+ * <p>What you give up: the {@code token_type} check and the jti denylist have to move
+ * into an {@code OAuth2TokenValidator} (see
+ * {@link com.ankurm.jwtauth.edge.AccessTokenTypeValidator}).
+ * What you gain: {@code BearerTokenAuthenticationFilter},
+ * {@code BearerTokenAuthenticationEntryPoint} and {@code BearerTokenAccessDeniedHandler}
+ * are wired for you, with the correct WWW-Authenticate headers on both 401 and 403.
+ *
+ * @see docs/09-manual-filter-vs-resource-server.md
+ */
+@Configuration
+@EnableWebSecurity
+@EnableMethodSecurity
+@Profile("resourceserver")
+public class ResourceServerSecurityConfig {
+
+    @Bean
+    public SecurityFilterChain apiFilterChain(HttpSecurity http) throws Exception {
+        http
+            .sessionManagement(session -> session
+                    .sessionCreationPolicy(SessionCreationPolicy.STATELESS))
+            .securityContext(context -> context
+                    .securityContextRepository(new NullSecurityContextRepository()))
+            .csrf(csrf -> csrf.disable())
+            .formLogin(form -> form.disable())
+            .httpBasic(basic -> basic.disable())
+            .authorizeHttpRequests(auth -> auth
+                    .requestMatchers("/api/public/**", "/api/auth/login", "/api/auth/refresh").permitAll()
+                    .requestMatchers("/.well-known/**", "/actuator/health").permitAll()
+                    .requestMatchers("/api/admin/**").hasRole("ADMIN")
+                    .anyRequest().authenticated())
+            // One line replaces the whole custom filter. The JwtDecoder bean is picked
+            // up automatically; BearerTokenAuthenticationFilter is inserted in the
+            // right place; 401 and 403 handlers come with it.
+            .oauth2ResourceServer(oauth2 -> oauth2
+                    .jwt(jwt -> jwt.jwtAuthenticationConverter(jwtAuthenticationConverter())));
+
+        return http.build();
+    }
+
+    /** Same authority mapping as the manual filter, expressed the framework's way. */
+    private Converter<Jwt, AbstractAuthenticationToken> jwtAuthenticationConverter() {
+        JwtGrantedAuthoritiesConverter scopes = new JwtGrantedAuthoritiesConverter();
+        scopes.setAuthoritiesClaimName("scope");
+        scopes.setAuthorityPrefix("SCOPE_");
+
+        JwtGrantedAuthoritiesConverter roles = new JwtGrantedAuthoritiesConverter();
+        roles.setAuthoritiesClaimName("roles");
+        roles.setAuthorityPrefix("ROLE_");
+
+        JwtAuthenticationConverter converter = new JwtAuthenticationConverter();
+        converter.setJwtGrantedAuthoritiesConverter(jwt -> {
+            List<GrantedAuthority> all = new ArrayList<>(scopes.convert(jwt));
+            all.addAll(roles.convert(jwt));
+            return all;
+        });
+        return converter;
+    }
+
+    /**
+     * Only registered under the {@code strict} profile - on purpose. Run without it
+     * and a refresh token authenticates as an access token; run with it and the same
+     * request is a 401. The built-in resource server has no opinion about your
+     * private claims until you give it one.
+     */
+    @Bean
+    @org.springframework.boot.autoconfigure.condition.ConditionalOnProperty(
+            name = "demo.validate-token-type", havingValue = "true")
+    public org.springframework.security.oauth2.core.OAuth2TokenValidator<
+            org.springframework.security.oauth2.jwt.Jwt> accessTokenTypeValidator() {
+        return new com.ankurm.jwtauth.edge.AccessTokenTypeValidator();
+    }
+
+    @Bean
+    public AuthenticationManager authenticationManager(UserDetailsService users,
+                                                       PasswordEncoder encoder) {
+        DaoAuthenticationProvider provider = new DaoAuthenticationProvider(users);
+        provider.setPasswordEncoder(encoder);
+        return new ProviderManager(provider);
+    }
+
+    /** Unused, kept as documentation of the alternative authority mapping. */
+    @SuppressWarnings("unused")
+    private GrantedAuthority example() {
+        return new SimpleGrantedAuthority("SCOPE_profile:read");
+    }
+}
--- a/jwt-authentication/src/main/java/com/ankurm/jwtauth/config/Rs256KeyConfig.java
+++ b/jwt-authentication/src/main/java/com/ankurm/jwtauth/config/Rs256KeyConfig.java
@@ -0,0 +1,120 @@
+package com.ankurm.jwtauth.config;
+
+import java.io.InputStream;
+import java.nio.charset.StandardCharsets;
+import java.security.KeyFactory;
+import java.security.interfaces.RSAPrivateKey;
+import java.security.interfaces.RSAPublicKey;
+import java.security.spec.PKCS8EncodedKeySpec;
+import java.security.spec.X509EncodedKeySpec;
+import java.util.Base64;
+import java.util.Map;
+
+import com.nimbusds.jose.jwk.JWKSet;
+import com.nimbusds.jose.jwk.RSAKey;
+import org.springframework.beans.factory.ObjectProvider;
+import org.springframework.beans.factory.annotation.Value;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.context.annotation.Profile;
+import org.springframework.core.io.ClassPathResource;
+import org.springframework.security.oauth2.jose.jws.SignatureAlgorithm;
+import org.springframework.security.oauth2.core.OAuth2TokenValidator;
+import org.springframework.security.oauth2.jwt.Jwt;
+import org.springframework.security.oauth2.jwt.JwtDecoder;
+import org.springframework.security.oauth2.jwt.JwtEncoder;
+import org.springframework.security.oauth2.jwt.NimbusJwtDecoder;
+import org.springframework.security.oauth2.jwt.NimbusJwtEncoder;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.RestController;
+
+/**
+ * RS256 variant: the private key signs, the public key verifies.
+ *
+ * <p>The public half is also published at {@code /.well-known/jwks.json} so a
+ * separate resource server could verify tokens without ever seeing the private key.
+ */
+@Configuration
+@Profile("rs256")
+public class Rs256KeyConfig {
+
+    private final RSAPublicKey publicKey;
+    private final RSAPrivateKey privateKey;
+    private final String keyId = "demo-rsa-2026-08";
+    private final String issuer;
+    private final String audience;
+
+    public Rs256KeyConfig(@Value("${demo.jwt.issuer}") String issuer,
+                          @Value("${demo.jwt.audience}") String audience) throws Exception {
+        this.issuer = issuer;
+        this.audience = audience;
+        this.privateKey = readPrivateKey("demo-private-key.pem");
+        this.publicKey = readPublicKey("demo-public-key.pem");
+    }
+
+    @Bean
+    public JwtEncoder jwtEncoder() {
+        // Note: the builder method is algorithm(..), not jwsAlgorithm(..), and there is
+        // no keyId(..) - the key id is set by post-processing the Nimbus JWK builder.
+        return NimbusJwtEncoder.withKeyPair(this.publicKey, this.privateKey)
+                .algorithm(SignatureAlgorithm.RS256)
+                .jwkPostProcessor(jwk -> jwk.keyID(this.keyId))
+                .build();
+    }
+
+    @Bean
+    public JwtDecoder jwtDecoder(ObjectProvider<OAuth2TokenValidator<Jwt>> extraValidators) {
+        NimbusJwtDecoder decoder = NimbusJwtDecoder.withPublicKey(this.publicKey)
+                .signatureAlgorithm(SignatureAlgorithm.RS256)  // pin it - see docs/07-edge-cases.md
+                .build();
+        decoder.setJwtValidator(JwtValidatorFactory.compose(this.issuer, this.audience, extraValidators));
+        return decoder;
+    }
+
+    /**
+     * A minimal JWKS endpoint. A real authorization server publishes this and the
+     * resource server points at it with {@code NimbusJwtDecoder.withJwkSetUri(...)},
+     * which then rotates keys automatically by {@code kid}.
+     */
+    @RestController
+    @Profile("rs256")
+    public static class JwkSetEndpoint {
+
+        private final JWKSet jwkSet;
+
+        public JwkSetEndpoint(Rs256KeyConfig keys) {
+            RSAKey rsaKey = new RSAKey.Builder(keys.publicKey)
+                    .keyID(keys.keyId)
+                    .build();
+            this.jwkSet = new JWKSet(rsaKey);
+        }
+
+        @GetMapping("/.well-known/jwks.json")
+        public Map<String, Object> keys() {
+            return this.jwkSet.toJSONObject();  // public parameters only
+        }
+    }
+
+    private static RSAPrivateKey readPrivateKey(String path) throws Exception {
+        byte[] der = pemBody(path, "PRIVATE KEY");
+        return (RSAPrivateKey) KeyFactory.getInstance("RSA")
+                .generatePrivate(new PKCS8EncodedKeySpec(der));
+    }
+
+    private static RSAPublicKey readPublicKey(String path) throws Exception {
+        byte[] der = pemBody(path, "PUBLIC KEY");
+        return (RSAPublicKey) KeyFactory.getInstance("RSA")
+                .generatePublic(new X509EncodedKeySpec(der));
+    }
+
+    private static byte[] pemBody(String path, String label) throws Exception {
+        try (InputStream in = new ClassPathResource(path).getInputStream()) {
+            String pem = new String(in.readAllBytes(), StandardCharsets.UTF_8);
+            String base64 = pem
+                    .replace("-----BEGIN " + label + "-----", "")
+                    .replace("-----END " + label + "-----", "")
+                    .replaceAll("\\s", "");
+            return Base64.getDecoder().decode(base64);
+        }
+    }
+}
--- a/jwt-authentication/src/main/java/com/ankurm/jwtauth/config/SecurityConfig.java
+++ b/jwt-authentication/src/main/java/com/ankurm/jwtauth/config/SecurityConfig.java
@@ -0,0 +1,140 @@
+package com.ankurm.jwtauth.config;
+
+import com.ankurm.jwtauth.auth.JwtAuthenticationFilter;
+import com.ankurm.jwtauth.auth.RevokedTokenStore;
+import org.springframework.beans.factory.annotation.Value;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.context.annotation.Profile;
+import org.springframework.security.authentication.AuthenticationManager;
+import org.springframework.security.authentication.ProviderManager;
+import org.springframework.security.authentication.dao.DaoAuthenticationProvider;
+import org.springframework.security.config.annotation.method.configuration.EnableMethodSecurity;
+import org.springframework.security.config.annotation.web.builders.HttpSecurity;
+import org.springframework.security.config.annotation.web.configuration.EnableWebSecurity;
+import org.springframework.security.config.http.SessionCreationPolicy;
+import org.springframework.security.core.userdetails.UserDetailsService;
+import org.springframework.security.crypto.password.PasswordEncoder;
+import org.springframework.security.oauth2.jwt.JwtDecoder;
+import org.springframework.security.oauth2.server.resource.web.access.BearerTokenAccessDeniedHandler;
+import org.springframework.security.oauth2.server.resource.web.BearerTokenAuthenticationEntryPoint;
+import org.springframework.security.web.AuthenticationEntryPoint;
+import org.springframework.security.web.SecurityFilterChain;
+import org.springframework.security.web.access.AccessDeniedHandler;
+import org.springframework.security.web.authentication.UsernamePasswordAuthenticationFilter;
+import org.springframework.security.web.context.NullSecurityContextRepository;
+
+/**
+ * The default chain: our own {@link JwtAuthenticationFilter} does the verifying.
+ *
+ * <p>Active unless the {@code resourceserver} profile is on. Compare with
+ * {@link ResourceServerSecurityConfig}, which deletes most of this file.
+ *
+ * @see docs/02-filter-chain-and-ordering.md
+ * @see docs/03-401-vs-403.md
+ */
+@Configuration
+@EnableWebSecurity
+@EnableMethodSecurity          // enables @PreAuthorize on controller methods
+@Profile("!resourceserver")
+public class SecurityConfig {
+
+    /**
+     * CSRF is off by default here (stateless bearer-token API). Flip
+     * {@code demo.csrf.enabled=true} to reproduce the "permitAll() still 403s" failure
+     * described in docs/04-csrf-permitall-403.md.
+     */
+    @Value("${demo.csrf.enabled:false}")
+    private boolean csrfEnabled;
+
+    @Bean
+    public SecurityFilterChain apiFilterChain(HttpSecurity http,
+                                              JwtDecoder jwtDecoder,
+                                              RevokedTokenStore revokedTokens,
+                                              AuthenticationEntryPoint entryPoint,
+                                              AccessDeniedHandler accessDeniedHandler) throws Exception {
+
+        JwtAuthenticationFilter jwtFilter =
+                new JwtAuthenticationFilter(jwtDecoder, revokedTokens, entryPoint);
+
+        http
+            // 1. No sessions, no session cookie, nothing to fix on the server.
+            .sessionManagement(session -> session
+                    .sessionCreationPolicy(SessionCreationPolicy.STATELESS))
+            .securityContext(context -> context
+                    .securityContextRepository(new NullSecurityContextRepository()))
+
+            // 2. CSRF. See the callout in docs/04 before you copy the disable() line.
+            .csrf(csrf -> {
+                if (this.csrfEnabled) {
+                    // Left at defaults on purpose: this is the failure, not the fix.
+                    // Every unsafe method now needs a CSRF token - including the
+                    // permitAll() login endpoint. See docs/04-csrf-permitall-403.md.
+                    csrf.csrfTokenRepository(
+                            org.springframework.security.web.csrf.CookieCsrfTokenRepository
+                                    .withHttpOnlyFalse());
+                }
+                else {
+                    // Correct for a bearer-token API: the browser never attaches
+                    // credentials automatically, so there is nothing to forge.
+                    csrf.disable();
+                }
+            })
+
+            // 3. Nothing browser-shaped: no login page, no basic auth popup.
+            .formLogin(form -> form.disable())
+            .httpBasic(basic -> basic.disable())
+            .logout(logout -> logout.disable())
+
+            // 4. Authorization. Evaluated by AuthorizationFilter, the LAST filter.
+            .authorizeHttpRequests(auth -> auth
+                    .requestMatchers("/api/public/**", "/api/auth/login", "/api/auth/refresh").permitAll()
+                    .requestMatchers("/.well-known/**", "/actuator/health").permitAll()
+                    .requestMatchers("/api/admin/**").hasRole("ADMIN")
+                    .anyRequest().authenticated())
+
+            // 5. What an authentication failure and an authorization failure look like.
+            .exceptionHandling(ex -> ex
+                    .authenticationEntryPoint(entryPoint)
+                    .accessDeniedHandler(accessDeniedHandler))
+
+            // 6. Position matters. Before UsernamePasswordAuthenticationFilter puts us
+            //    ahead of AnonymousAuthenticationFilter and ExceptionTranslationFilter,
+            //    which is what we want. addFilterAfter(..., AuthorizationFilter.class)
+            //    would run after the decision has already been made.
+            .addFilterBefore(jwtFilter, UsernamePasswordAuthenticationFilter.class);
+
+        return http.build();
+    }
+
+    /**
+     * 401, with a {@code WWW-Authenticate: Bearer ...} header carrying the
+     * RFC 6750 error code. Reused by the filter so unauthenticated responses
+     * are identical whether they come from the filter or from
+     * {@code ExceptionTranslationFilter}.
+     */
+    @Bean
+    public AuthenticationEntryPoint bearerTokenEntryPoint() {
+        BearerTokenAuthenticationEntryPoint entryPoint = new BearerTokenAuthenticationEntryPoint();
+        entryPoint.setRealmName("jwt-auth-demo");
+        return entryPoint;
+    }
+
+    /** 403, with {@code error="insufficient_scope"} in WWW-Authenticate. */
+    @Bean
+    public AccessDeniedHandler bearerTokenAccessDeniedHandler() {
+        return new BearerTokenAccessDeniedHandler();
+    }
+
+    /**
+     * The login endpoint needs this. Once you define a SecurityFilterChain bean,
+     * Boot no longer auto-configures an AuthenticationManager, so build one.
+     */
+    @Bean
+    public AuthenticationManager authenticationManager(UserDetailsService users,
+                                                       PasswordEncoder encoder) {
+        DaoAuthenticationProvider provider = new DaoAuthenticationProvider(users);
+        provider.setPasswordEncoder(encoder);
+        return new ProviderManager(provider);
+    }
+}
--- a/jwt-authentication/src/main/java/com/ankurm/jwtauth/diag/FilterChainReport.java
+++ b/jwt-authentication/src/main/java/com/ankurm/jwtauth/diag/FilterChainReport.java
@@ -0,0 +1,55 @@
+package com.ankurm.jwtauth.diag;
+
+import java.util.List;
+import java.util.Map;
+
+import jakarta.servlet.Filter;
+import jakarta.servlet.http.HttpServletRequest;
+import org.springframework.security.web.FilterChainProxy;
+import org.springframework.security.web.SecurityFilterChain;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.RestController;
+
+/**
+ * Prints the real filter order at runtime instead of the one you remember.
+ *
+ * <p>{@code GET /api/public/filters} - deliberately under {@code /api/public} so it is
+ * reachable without a token. Delete this class before shipping: it tells an attacker
+ * exactly which filters guard the application.
+ */
+@RestController
+public class FilterChainReport {
+
+    private final FilterChainProxy filterChainProxy;
+
+    public FilterChainReport(FilterChainProxy filterChainProxy) {
+        this.filterChainProxy = filterChainProxy;
+    }
+
+    @GetMapping("/api/public/filters")
+    public List<Map<String, Object>> filters(HttpServletRequest request) {
+        return this.filterChainProxy.getFilterChains().stream()
+                .map(chain -> Map.<String, Object>of(
+                        "chain", chain.toString(),
+                        "matchesThisRequest", matches(chain, request),
+                        "filters", chain.getFilters().stream()
+                                .map(f -> f.getClass().getSimpleName())
+                                .toList()))
+                .toList();
+    }
+
+    private boolean matches(SecurityFilterChain chain, HttpServletRequest request) {
+        try {
+            return chain.matches(request);
+        }
+        catch (RuntimeException ex) {
+            return false;
+        }
+    }
+
+    /** Unused; shows the type the list actually holds. */
+    @SuppressWarnings("unused")
+    private Class<?> filterType(Filter filter) {
+        return filter.getClass();
+    }
+}
--- a/jwt-authentication/src/main/java/com/ankurm/jwtauth/edge/AccessTokenTypeValidator.java
+++ b/jwt-authentication/src/main/java/com/ankurm/jwtauth/edge/AccessTokenTypeValidator.java
@@ -0,0 +1,39 @@
+package com.ankurm.jwtauth.edge;
+
+import com.ankurm.jwtauth.auth.TokenService;
+import org.springframework.security.oauth2.core.OAuth2Error;
+import org.springframework.security.oauth2.core.OAuth2TokenValidator;
+import org.springframework.security.oauth2.core.OAuth2TokenValidatorResult;
+import org.springframework.security.oauth2.jwt.Jwt;
+
+/**
+ * Edge case: a refresh token is a valid access token unless you say otherwise.
+ *
+ * <p>Both are signed by the same key, both carry a valid {@code exp}, both pass every
+ * default validator. If the only difference is the TTL, a stolen refresh token is a
+ * long-lived access token. This validator is the resource-server equivalent of the
+ * {@code token_type} check inside {@code JwtAuthenticationFilter}.
+ *
+ * <pre>
+ * NimbusJwtDecoder decoder = NimbusJwtDecoder.withSecretKey(key).build();
+ * decoder.setJwtValidator(new DelegatingOAuth2TokenValidator&lt;&gt;(
+ *         JwtValidators.createDefaultWithIssuer(issuer),
+ *         new AccessTokenTypeValidator()));
+ * </pre>
+ *
+ * @see docs/07-edge-cases.md
+ */
+public class AccessTokenTypeValidator implements OAuth2TokenValidator<Jwt> {
+
+    private static final OAuth2Error ERROR = new OAuth2Error(
+            "invalid_token",
+            "Expected a token with token_type=access",
+            "https://ankurm.com/spring-security-7-1-jwt-authentication-guide/");
+
+    @Override
+    public OAuth2TokenValidatorResult validate(Jwt jwt) {
+        return TokenService.ACCESS.equals(jwt.getClaimAsString("token_type"))
+                ? OAuth2TokenValidatorResult.success()
+                : OAuth2TokenValidatorResult.failure(ERROR);
+    }
+}
--- a/jwt-authentication/src/main/java/com/ankurm/jwtauth/edge/AsyncPropagationDemo.java
+++ b/jwt-authentication/src/main/java/com/ankurm/jwtauth/edge/AsyncPropagationDemo.java
@@ -0,0 +1,50 @@
+package com.ankurm.jwtauth.edge;
+
+import java.util.Map;
+import java.util.concurrent.Callable;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+
+import org.springframework.security.concurrent.DelegatingSecurityContextExecutorService;
+import org.springframework.security.core.Authentication;
+import org.springframework.security.core.context.SecurityContextHolder;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.RestController;
+
+/**
+ * Edge case: the {@code SecurityContext} lives in a {@code ThreadLocal}, so it does
+ * not cross a thread boundary on its own.
+ *
+ * <p>{@code GET /api/async-demo} runs the same lookup on a plain executor and on a
+ * {@code DelegatingSecurityContextExecutorService}, and returns both answers. The
+ * plain one is {@code null} - and {@code null} here means an authenticated user's
+ * background work runs unauthenticated, which usually surfaces as a
+ * {@code AuthenticationCredentialsNotFoundException} far from the cause.
+ *
+ * @see docs/07-edge-cases.md#async
+ */
+@RestController
+public class AsyncPropagationDemo {
+
+    @GetMapping("/api/async-demo")
+    public Map<String, Object> asyncDemo() throws Exception {
+        Callable<String> readPrincipal = () -> {
+            Authentication auth = SecurityContextHolder.getContext().getAuthentication();
+            return auth == null ? "null (context did not cross the thread)" : auth.getName();
+        };
+
+        ExecutorService plain = Executors.newVirtualThreadPerTaskExecutor();
+        ExecutorService wrapped = new DelegatingSecurityContextExecutorService(
+                Executors.newVirtualThreadPerTaskExecutor());
+        try {
+            return Map.of(
+                    "onRequestThread", readPrincipal.call(),
+                    "onPlainExecutor", plain.submit(readPrincipal).get(),
+                    "onDelegatingExecutor", wrapped.submit(readPrincipal).get());
+        }
+        finally {
+            plain.shutdown();
+            wrapped.shutdown();
+        }
+    }
+}
--- a/jwt-authentication/src/main/java/com/ankurm/jwtauth/edge/AudienceValidator.java
+++ b/jwt-authentication/src/main/java/com/ankurm/jwtauth/edge/AudienceValidator.java
@@ -0,0 +1,39 @@
+package com.ankurm.jwtauth.edge;
+
+import java.util.List;
+
+import org.springframework.security.oauth2.core.OAuth2Error;
+import org.springframework.security.oauth2.core.OAuth2TokenValidator;
+import org.springframework.security.oauth2.core.OAuth2TokenValidatorResult;
+import org.springframework.security.oauth2.jwt.Jwt;
+import org.springframework.security.oauth2.jwt.JwtClaimNames;
+import org.springframework.security.oauth2.jwt.JwtClaimValidator;
+
+/**
+ * Edge case: {@code aud} is NOT validated by default.
+ *
+ * <p>{@code JwtValidators.createDefaultWithIssuer(issuer)} checks {@code exp},
+ * {@code nbf} and {@code iss} - not {@code aud}. In a multi-service estate where every
+ * service trusts the same issuer, that means a token minted for the reporting API is
+ * accepted by the payments API. Confused-deputy, by default.
+ *
+ * @see docs/07-edge-cases.md#audience
+ */
+public final class AudienceValidator {
+
+    private AudienceValidator() { }
+
+    public static OAuth2TokenValidator<Jwt> forAudience(String expected) {
+        return new JwtClaimValidator<List<String>>(JwtClaimNames.AUD,
+                aud -> aud != null && aud.contains(expected));
+    }
+
+    /** The long-hand equivalent, for readers who prefer to see the shape. */
+    public static OAuth2TokenValidator<Jwt> explicit(String expected) {
+        OAuth2Error error = new OAuth2Error("invalid_token",
+                "The required audience " + expected + " is missing", null);
+        return jwt -> jwt.getAudience() != null && jwt.getAudience().contains(expected)
+                ? OAuth2TokenValidatorResult.success()
+                : OAuth2TokenValidatorResult.failure(error);
+    }
+}
--- a/jwt-authentication/src/main/java/com/ankurm/jwtauth/web/ApiControllers.java
+++ b/jwt-authentication/src/main/java/com/ankurm/jwtauth/web/ApiControllers.java
@@ -0,0 +1,62 @@
+package com.ankurm.jwtauth.web;
+
+import java.util.List;
+import java.util.Map;
+
+import org.springframework.security.access.prepost.PreAuthorize;
+import org.springframework.security.core.Authentication;
+import org.springframework.security.core.GrantedAuthority;
+import org.springframework.security.oauth2.jwt.Jwt;
+import org.springframework.security.oauth2.server.resource.authentication.JwtAuthenticationToken;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.RestController;
+
+/**
+ * Four endpoints, chosen so every authorization outcome is reachable from curl:
+ * <ul>
+ *   <li>{@code /api/public/ping} - permitAll, works with no token.</li>
+ *   <li>{@code /api/me} - authenticated, 401 without a token.</li>
+ *   <li>{@code /api/admin/stats} - hasRole('ADMIN'), 403 for a valid non-admin token.</li>
+ *   <li>{@code /api/reports} - hasAuthority('SCOPE_admin:read'), the scope-based twin.</li>
+ * </ul>
+ */
+@RestController
+public class ApiControllers {
+
+    @GetMapping("/api/public/ping")
+    public Map<String, Object> ping() {
+        return Map.of("status", "up", "authenticationRequired", false);
+    }
+
+    @GetMapping("/api/me")
+    public Map<String, Object> me(Authentication authentication) {
+        Map<String, Object> body = new java.util.LinkedHashMap<>();
+        body.put("name", authentication.getName());
+        body.put("authorities", authentication.getAuthorities().stream()
+                .map(GrantedAuthority::getAuthority).sorted().toList());
+        body.put("authenticationType", authentication.getClass().getSimpleName());
+
+        if (authentication instanceof JwtAuthenticationToken jwtAuth) {
+            Jwt jwt = jwtAuth.getToken();
+            body.put("jti", jwt.getId());
+            body.put("issuer", jwt.getIssuer() == null ? null : jwt.getIssuer().toString());
+            body.put("audience", jwt.getAudience());
+            body.put("issuedAt", String.valueOf(jwt.getIssuedAt()));
+            body.put("expiresAt", String.valueOf(jwt.getExpiresAt()));
+            body.put("algorithm", jwt.getHeaders().get("alg"));
+            body.put("keyId", jwt.getHeaders().get("kid"));
+        }
+        return body;
+    }
+
+    @GetMapping("/api/admin/stats")
+    public Map<String, Object> adminStats() {
+        return Map.of("activeUsers", 3, "requiredRole", "ROLE_ADMIN");
+    }
+
+    @GetMapping("/api/reports")
+    @PreAuthorize("hasAuthority('SCOPE_admin:read')")
+    public List<String> reports() {
+        return List.of("q1-revenue", "q2-revenue");
+    }
+}
--- a/jwt-authentication/src/main/resources/application-csrfon.yaml
+++ b/jwt-authentication/src/main/resources/application-csrfon.yaml
@@ -0,0 +1,5 @@
+# Run with --spring.profiles.active=hs256,csrfon to reproduce the failure in
+# docs/04-csrf-permitall-403.md: a permitAll() login endpoint answering 403.
+demo:
+  csrf:
+    enabled: true
--- a/jwt-authentication/src/main/resources/application-shortlived.yaml
+++ b/jwt-authentication/src/main/resources/application-shortlived.yaml
@@ -0,0 +1,6 @@
+# Run with --spring.profiles.active=hs256,shortlived to observe expiry and
+# clock-skew behaviour without waiting 15 minutes.
+demo:
+  jwt:
+    access-token-ttl: 2s
+    refresh-token-ttl: 30s
--- a/jwt-authentication/src/main/resources/application-strict.yaml
+++ b/jwt-authentication/src/main/resources/application-strict.yaml
@@ -0,0 +1,5 @@
+# Run with --spring.profiles.active=hs256,resourceserver,strict to wire the
+# AccessTokenTypeValidator into the JwtDecoder. Without it, the built-in resource
+# server happily accepts a refresh token as an access token - see docs/07.
+demo:
+  validate-token-type: true
--- a/jwt-authentication/src/main/resources/application-trace.yaml
+++ b/jwt-authentication/src/main/resources/application-trace.yaml
@@ -0,0 +1,5 @@
+# Run with --spring.profiles.active=hs256,trace to see every filter decision.
+logging:
+  level:
+    org.springframework.security: TRACE
+    org.springframework.security.web.FilterChainProxy: TRACE
--- a/jwt-authentication/src/main/resources/application.yaml
+++ b/jwt-authentication/src/main/resources/application.yaml
@@ -0,0 +1,28 @@
+spring:
+  application:
+    name: jwt-auth-demo
+  profiles:
+    # hs256 = symmetric signing, manual = hand-written OncePerRequestFilter.
+    # Override with: --spring.profiles.active=rs256,resourceserver
+    default: hs256
+
+server:
+  port: 8080
+  error:
+    include-message: always
+
+demo:
+  csrf:
+    # true reproduces the "permitAll() still 403s" failure from docs/04.
+    enabled: false
+  jwt:
+    issuer: https://jwt-auth-demo.ankurm.com
+    audience: jwt-auth-demo-api
+    access-token-ttl: 15m
+    refresh-token-ttl: 8h
+    # 32+ bytes. Demo value only - a real deployment reads this from a secret manager.
+    hmac-secret: ankurm-demo-hmac-secret-key-please-rotate-me-32b
+
+logging:
+  level:
+    org.springframework.security: INFO
--- a/jwt-authentication/src/main/resources/demo-private-key.pem
+++ b/jwt-authentication/src/main/resources/demo-private-key.pem
@@ -0,0 +1,28 @@
+-----BEGIN PRIVATE KEY-----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+-----END PRIVATE KEY-----
--- a/jwt-authentication/src/main/resources/demo-public-key.pem
+++ b/jwt-authentication/src/main/resources/demo-public-key.pem
@@ -0,0 +1,9 @@
+-----BEGIN PUBLIC KEY-----
+MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEA5NEDQPQW0Gz6iR5+UNl7
+J7660/Psd5q1f5VamK9KTS9f6YhPPIG8mfi6zWe8XmxxdR/Bd2yaX+v/Wz6MgeFL
+bBVkRFfve/zVnq4+kgjhn8UaRK1iU0C1j+7SahD73hHqGaOjAlFNro5ygjGAcVL8
+RGVMxRMy4aaTAm3KB4EdG2hJFxyfCBqtkwsHTM/DXcoFTLTZ2bI+hPhN6uBxk7yk
+FaCnQ47yrKSM6kn0ul0dp22AK/4mP1SRDnnr3Da5GFhMKtBqy/GgXcJ9WTpxIYhl
+r8B5modtb5S34900VPScpoXiJdUhghxEpXbb1W/PlpVIElISHzldnwWOogdPncO0
+zQIDAQAB
+-----END PUBLIC KEY-----
--- a/jwt-authentication/src/test/java/com/ankurm/jwtauth/AuthenticationFlowTests.java
+++ b/jwt-authentication/src/test/java/com/ankurm/jwtauth/AuthenticationFlowTests.java
@@ -0,0 +1,142 @@
+package com.ankurm.jwtauth;
+
+import com.ankurm.jwtauth.auth.RevokedTokenStore;
+import org.junit.jupiter.api.Test;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.webmvc.test.autoconfigure.AutoConfigureMockMvc;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.http.MediaType;
+import org.springframework.test.context.ActiveProfiles;
+import org.springframework.test.web.servlet.MockMvc;
+import org.springframework.test.web.servlet.MvcResult;
+
+import java.util.Map;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get;
+import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.post;
+import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.header;
+import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;
+
+/**
+ * The 401-vs-403 contract, pinned as tests.
+ *
+ * @see docs/03-401-vs-403.md
+ */
+@SpringBootTest
+@AutoConfigureMockMvc
+@ActiveProfiles("hs256")
+class AuthenticationFlowTests {
+
+    @Autowired MockMvc mvc;
+    @Autowired RevokedTokenStore revokedTokens;
+
+    private static final tools.jackson.databind.ObjectMapper JSON =
+            new tools.jackson.databind.ObjectMapper();
+
+    private Map<String, String> login(String user, String password) throws Exception {
+        MvcResult result = this.mvc.perform(post("/api/auth/login")
+                        .contentType(MediaType.APPLICATION_JSON)
+                        .content("{\"username\":\"%s\",\"password\":\"%s\"}".formatted(user, password)))
+                .andExpect(status().isOk())
+                .andReturn();
+        return JSON.readValue(result.getResponse().getContentAsString(),
+                new tools.jackson.core.type.TypeReference<Map<String, String>>() { });
+    }
+
+    @Test
+    void publicEndpointNeedsNoToken() throws Exception {
+        this.mvc.perform(get("/api/public/ping")).andExpect(status().isOk());
+    }
+
+    @Test
+    void missingTokenIs401NotA403() throws Exception {
+        this.mvc.perform(get("/api/me"))
+                .andExpect(status().isUnauthorized())
+                .andExpect(header().string("WWW-Authenticate",
+                        org.hamcrest.Matchers.containsString("Bearer")));
+    }
+
+    @Test
+    void validTokenWithoutTheRoleIs403NotA401() throws Exception {
+        String token = login("alice", "alice-password").get("accessToken");
+        this.mvc.perform(get("/api/admin/stats").header("Authorization", "Bearer " + token))
+                .andExpect(status().isForbidden())
+                .andExpect(header().string("WWW-Authenticate",
+                        org.hamcrest.Matchers.containsString("insufficient_scope")));
+    }
+
+    @Test
+    void adminTokenReachesAdminEndpoint() throws Exception {
+        String token = login("root", "root-password").get("accessToken");
+        this.mvc.perform(get("/api/admin/stats").header("Authorization", "Bearer " + token))
+                .andExpect(status().isOk());
+    }
+
+    @Test
+    void tamperedSignatureIs401WithInvalidToken() throws Exception {
+        String token = login("alice", "alice-password").get("accessToken");
+        String tampered = token.substring(0, token.length() - 4) + "AAAA";
+        this.mvc.perform(get("/api/me").header("Authorization", "Bearer " + tampered))
+                .andExpect(status().isUnauthorized())
+                .andExpect(header().string("WWW-Authenticate",
+                        org.hamcrest.Matchers.containsString("invalid_token")));
+    }
+
+    @Test
+    void refreshTokenIsNotAnAccessToken() throws Exception {
+        String refresh = login("alice", "alice-password").get("refreshToken");
+        this.mvc.perform(get("/api/me").header("Authorization", "Bearer " + refresh))
+                .andExpect(status().isUnauthorized());
+    }
+
+    @Test
+    void badPasswordIs401AndSaysNothingUseful() throws Exception {
+        this.mvc.perform(post("/api/auth/login")
+                        .contentType(MediaType.APPLICATION_JSON)
+                        .content("{\"username\":\"alice\",\"password\":\"nope\"}"))
+                .andExpect(status().isUnauthorized());
+    }
+
+    @Test
+    void lockedAccountIsIndistinguishableFromABadPassword() throws Exception {
+        MvcResult locked = this.mvc.perform(post("/api/auth/login")
+                        .contentType(MediaType.APPLICATION_JSON)
+                        .content("{\"username\":\"locked\",\"password\":\"locked-password\"}"))
+                .andExpect(status().isUnauthorized()).andReturn();
+        MvcResult wrong = this.mvc.perform(post("/api/auth/login")
+                        .contentType(MediaType.APPLICATION_JSON)
+                        .content("{\"username\":\"alice\",\"password\":\"nope\"}"))
+                .andExpect(status().isUnauthorized()).andReturn();
+
+        assertThat(locked.getResponse().getContentAsString())
+                .isEqualTo(wrong.getResponse().getContentAsString());
+    }
+
+    @Test
+    void revokedTokenIsRefusedEvenThoughTheSignatureIsStillValid() throws Exception {
+        String token = login("alice", "alice-password").get("accessToken");
+        this.mvc.perform(get("/api/me").header("Authorization", "Bearer " + token))
+                .andExpect(status().isOk());
+
+        this.mvc.perform(post("/api/auth/logout").header("Authorization", "Bearer " + token))
+                .andExpect(status().isNoContent());
+
+        this.mvc.perform(get("/api/me").header("Authorization", "Bearer " + token))
+                .andExpect(status().isUnauthorized());
+    }
+
+    @Test
+    void spentRefreshTokenCannotBeReplayed() throws Exception {
+        String refresh = login("alice", "alice-password").get("refreshToken");
+        this.mvc.perform(post("/api/auth/refresh")
+                        .contentType(MediaType.APPLICATION_JSON)
+                        .content("{\"refreshToken\":\"%s\"}".formatted(refresh)))
+                .andExpect(status().isOk());
+        this.mvc.perform(post("/api/auth/refresh")
+                        .contentType(MediaType.APPLICATION_JSON)
+                        .content("{\"refreshToken\":\"%s\"}".formatted(refresh)))
+                .andExpect(status().isUnauthorized());
+    }
+
+}
--- a/jwt-authentication/src/test/java/com/ankurm/jwtauth/CsrfBreaksPermitAllTests.java
+++ b/jwt-authentication/src/test/java/com/ankurm/jwtauth/CsrfBreaksPermitAllTests.java
@@ -0,0 +1,59 @@
+package com.ankurm.jwtauth;
+
+import org.junit.jupiter.api.Test;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.webmvc.test.autoconfigure.AutoConfigureMockMvc;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.http.MediaType;
+import org.springframework.security.web.FilterChainProxy;
+import org.springframework.test.context.ActiveProfiles;
+import org.springframework.test.web.servlet.MockMvc;
+
+import java.util.List;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.springframework.security.test.web.servlet.request.SecurityMockMvcRequestPostProcessors.csrf;
+import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.post;
+import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;
+
+/**
+ * Pins the failure described in docs/04-csrf-permitall-403.md, and the two
+ * facts that explain it.
+ */
+@SpringBootTest
+@AutoConfigureMockMvc
+@ActiveProfiles({"hs256", "csrfon"})
+class CsrfBreaksPermitAllTests {
+
+    @Autowired MockMvc mvc;
+    @Autowired FilterChainProxy filterChainProxy;
+
+    @Test
+    void permitAllLoginStillReturns403WhenCsrfIsOn() throws Exception {
+        this.mvc.perform(post("/api/auth/login")
+                        .contentType(MediaType.APPLICATION_JSON)
+                        .content("{\"username\":\"alice\",\"password\":\"alice-password\"}"))
+                .andExpect(status().isForbidden());
+    }
+
+    @Test
+    void theSameRequestWithACsrfTokenSucceeds() throws Exception {
+        this.mvc.perform(post("/api/auth/login").with(csrf())
+                        .contentType(MediaType.APPLICATION_JSON)
+                        .content("{\"username\":\"alice\",\"password\":\"alice-password\"}"))
+                .andExpect(status().isOk());
+    }
+
+    @Test
+    void csrfFilterRunsLongBeforeAuthorizationFilter() {
+        List<String> filters = this.filterChainProxy.getFilterChains().getFirst()
+                .getFilters().stream().map(f -> f.getClass().getSimpleName()).toList();
+
+        int csrf = filters.indexOf("CsrfFilter");
+        int authorization = filters.indexOf("AuthorizationFilter");
+
+        assertThat(csrf).isNotNegative();
+        assertThat(authorization).isEqualTo(filters.size() - 1);
+        assertThat(csrf).isLessThan(authorization);
+    }
+}