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

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."