Ankur Mhatre
4dc45d5e00
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
59 lines
2.6 KiB
Bash
Executable File
59 lines
2.6 KiB
Bash
Executable File
#!/usr/bin/env bash
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# What an unknown kid costs the issuer.
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#
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# Spring Security builds its JWKSource with rateLimited(false), overriding Nimbus's own
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# default of a 30-second minimum interval between forced refreshes. Nothing then stands
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# between a token bearing an unrecognised kid and an HTTP request to the issuer.
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set -eu
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. "$(dirname "$0")/lib.sh"
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PROFILES="${1:-unknown}"
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N="${2:-25}"
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head1 "resource server profiles: $PROFILES"
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echo "Baseline: $N requests with a VALID token, whose kid is in the cached JWK Set."
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curl -s -X POST "$STUB/admin/reset-counter" >/dev/null
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GOOD=$(stub_token "sub=alice&aud=reports-api")
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curl -s -o /dev/null -H "Authorization: Bearer $GOOD" "$RS/api/me" # warm
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curl -s -X POST "$STUB/admin/reset-counter" >/dev/null
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for i in $(seq 1 "$N"); do
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curl -s -o /dev/null -H "Authorization: Bearer $GOOD" "$RS/api/me"
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done
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echo " requests to the resource server : $N"
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echo " fetches of /jwks.json : $(stub_fetches)"
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echo
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echo "Now $N requests carrying a token whose kid has never existed."
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echo "Each one is refused - but look at what it costs the issuer first."
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curl -s -X POST "$STUB/admin/reset-counter" >/dev/null
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for i in $(seq 1 "$N"); do
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BAD=$(curl -s -X POST "$STUB/token/unknown-kid")
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curl -s -o /dev/null -H "Authorization: Bearer $BAD" "$RS/api/me"
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done
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FETCHES=$(stub_fetches)
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echo " requests to the resource server : $N"
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echo " fetches of /jwks.json : $FETCHES"
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echo
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echo "Every rejected request became a request to the authorization server. An attacker who"
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echo "can reach an unauthenticated endpoint of your resource server can point that ratio at"
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echo "your identity provider, from one connection, using tokens that are never valid."
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echo
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echo "And it does not need an authenticated endpoint. /api/public/ping is permitAll()."
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curl -s -X POST "$STUB/admin/reset-counter" >/dev/null
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for i in $(seq 1 "$N"); do
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BAD=$(curl -s -X POST "$STUB/token/unknown-kid")
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curl -s -o /dev/null -H "Authorization: Bearer $BAD" "$RS/api/public/ping"
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done
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echo " requests to /api/public/ping : $N"
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echo " fetches of /jwks.json : $(stub_fetches)"
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echo
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echo "A permitAll() endpoint still evaluates a bearer token if one is present, because"
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echo "BearerTokenAuthenticationFilter runs before any authorization rule. Presenting a"
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echo "broken token to a public endpoint gets a 401 from the public endpoint - and a"
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echo "JWKS fetch on the way."
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call "GET /api/public/ping with an unknown kid" "$RS/api/public/ping" "$(curl -s -X POST "$STUB/token/unknown-kid")"
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echo
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echo "The status returned to the caller is unremarkable:"
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BAD=$(curl -s -X POST "$STUB/token/unknown-kid")
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call "GET /api/me with an unknown kid" "$RS/api/me" "$BAD"
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