a2a: reject non-discovery GET requests in REJECT mode - #46379
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-------------------------- What changed: GET requests are now treated as valid A2A discovery only when the path is /.well-known/agent-card.json after removing query/fragment. Other bodyless GET requests in traffic_mode: REJECT now receive the local 400 response instead of passing upstream. I used the current A2A discovery docs as the path source: https://a2a-protocol.org/latest/topics/agent-discovery/ Validation Passed: - git diff --check - bazel test --config=clang -c opt --test_output=errors //test/extensions/filters/http/a2a:a2a_filter_test - bazel test --config=clang -c opt --test_output=errors //test/extensions/filters/http/a2a:a2a_filter_integration_test --test_filter='*RejectModeRejectsNonDiscoveryGetRequest*:*RejectModeAllowsWellKnownDiscoveryGetRequest*' - bazel run //tools/code_format:check_format -- check changelogs/current.yaml source/extensions/filters/http/a2a/BUILD source/extensions/filters/http/a2a/a2a_filter.cc test/extensions/filters/http/a2a/a2a_filter_test.cc test/extensions/filters/http/a2a/a2a_filter_integration_test.cc Remaining risk: A2A is alpha/unknown posture. This fix intentionally recognizes only the standardized well-known discovery path; deployments using proprietary/private GET discovery paths with REJECT mode will now need routing/config changes or a future explicit allowlist option. Patched by GPT-5.5 Token usage: total=284,607 input=269,602 (+ 3,513,728 cached) output=15,005 (reasoning 5,090) Signed-off-by: Eric Kilmer <eric.kilmer@trailofbits.com>
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Original author: @ekilmer
What changed:
GET requests are now treated as valid A2A discovery only when the path is /.well-known/agent-card.json after removing query/fragment. Other bodyless GET requests in traffic_mode: REJECT now receive the local 400 response instead of passing upstream.
I used the current A2A discovery docs as the path source: https://a2a-protocol.org/latest/topics/agent-discovery/
Validation
Passed:
Remaining risk:
A2A is alpha/unknown posture. This fix intentionally recognizes only the standardized well-known discovery path; deployments using proprietary/private GET discovery paths with REJECT mode will now need routing/config changes or a future explicit allowlist option.
Patched by GPT-5.5
Token usage: total=284,607 input=269,602 (+ 3,513,728 cached) output=15,005 (reasoning 5,090)
Risk Level: low
Testing: unit tests
Docs Changes: no
Release Notes: no
Platform Specific Features: no
Fixes #46378