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## main #4670 +/- ##
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- Coverage 68.70% 68.65% -0.05%
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jhrozek
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Apr 8, 2026
AWS MCP Server no longer uses aws-mcp:* IAM actions. Authorization now happens at the AWS service level using two new condition keys: aws:ViaAWSMCPService and aws:CalledViaAWSMCP. - Replace aws-mcp:* permission model explanation with new single-layer model and document both condition keys - Update default role policy to use sts:GetCallerIdentity scoped to aws:ViaAWSMCPService with a BoolIfExists deny guardrail - Update S3 role policy to use service-level actions with aws:CalledViaAWSMCP condition - Add security best practices section covering the deny guardrail pattern, BoolIfExists truth table, and condition key guidance - Update troubleshooting section to reflect service-level errors - Add missing service: aws-mcp field to MCPExternalAuthConfig example - Add resourceUrl to MCPRemoteProxy oidcConfig example for OAuth protected resource discovery Depends on stacklok/toolhive#4670 (SigV4 proxy header fix). Fixes #587 Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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ChrisJBurns
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Apr 8, 2026
When requests arrive through a gateway (e.g. ngrok), `X-Forwarded-*` headers get signed by SigV4. Then `httputil.ReverseProxy.SetXForwarded()` rewrites those values, causing AWS to reject with 401 due to signature mismatch. Strip `X-Forwarded-For`/`Host`/`Proto`, `X-Real-Ip`, and `Forwarded` (RFC 7239) from the signing clone before computing the signature. This regressed in 0791876 ("Bump Go to 1.26.0", #4040) which refactored the transparent proxy from `httputil.NewSingleHostReverseProxy` (using `Director`) to `&httputil.ReverseProxy{Rewrite: ...}`. The new `Rewrite` callback calls `pr.SetXForwarded()`, which injects `X-Forwarded-*` headers on the outbound request — something the old `Director`-based approach did not do. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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When requests arrive through a gateway (e.g. ngrok),
X-Forwarded-*headers get signed by SigV4. Thenhttputil.ReverseProxy.SetXForwarded()rewrites those values, causing AWS to reject with 401 due to signature mismatch. StripX-Forwarded-For/Host/Proto,X-Real-Ip, andForwarded(RFC 7239) from the signing clone before computing the signature.This regressed in 0791876 ("Bump Go to 1.26.0", #4040) which refactored the transparent proxy from
httputil.NewSingleHostReverseProxy(usingDirector) to&httputil.ReverseProxy{Rewrite: ...}. The newRewritecallback callspr.SetXForwarded(), which injectsX-Forwarded-*headers on the outbound request — something the oldDirector-based approach did not do.