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fix(mcp): bound OBO token exchange by the server timeout; record a failed re-exchange as dispatched - #1362
Three follow-ups to the Entra On-Behalf-Of token exchange from #1361.
Fixes api7/AISIX-Cloud#1898
The exchange is now bounded by the server's timeout_ms. Before, the exchange initialize / server/discover runs up front on /mcp/{server} only had the token client's global 30 s cap, so a slow identity provider held the client's first request well past the timeout the operator configured. The exchange on a tool call had a related problem: it ran inside the connect (or, for type: openapi, the tool-call) deadline, so running out of it surfaced as a generic upstream connect failure instead of the identity provider being unavailable. Every exchange site now uses the same per-server deadline as the server's other upstream calls (timeout_ms, 30 s when unset; the token endpoint client keeps its own 30 s request cap, so a timeout_ms above 30 s does not extend an exchange):
initialize / server/discover preflight, type: mcp and type: openapi: bounded by timeout_ms from when the preflight starts.
type: mcp tool call or tool list: the exchange shares one deadline with the connect that follows it. The credential is now obtained before the session is opened, against that deadline, so an exchange that runs out of it is reported as such. The oauth2 client-credentials mint on the same path keeps its existing "connect timed out" outcome.
type: openapi tool call: the call's deadline now bounds each network step on its own (credential, request, response body) instead of wrapping the whole call, for the same reason. A slow REST API is still "tool call timed out" as before.
The re-exchange after an upstream 401 is bounded the same way as the attempt it belongs to.
Running out of the deadline is a 503 token_exchange_unavailable on /mcp/{server}, like any other identity-provider unavailability; the aggregated /mcp keeps absorbing it as that server's failure. Single-flight is unchanged: the exchange runs to completion in its own task, so a request that gives up does not cancel it, the other requests waiting on it get its outcome, and a token it obtains is cached for the next request.
A failed re-exchange after an upstream 401 is recorded as dispatched. The usage event's dispatched flag means "this event describes work that reached an upstream", and it decides whether the event keeps its upstream latency and gets an upstream span. When the upstream rejected the exchanged token and the re-exchange then failed, the 503's tool-call event was recorded as not dispatched, so it showed upstream_latency_ms: 0 even though the upstream had been contacted. The bridges now carry whether the failing exchange followed upstream contact (TokenExchangeError::reached_upstream), and the event follows it. A failure on the first exchange is still not dispatched.
The two token caches share one implementation.token_cache::TokenCache holds the tokens for both the OBO exchange and the oauth2 client-credentials grant. It is a pure refactor: each grant keeps its own key derivation and its own process-global instance, the TTL rule is the same (expires_in capped at 30 days, 3600 s when absent, not reused within 60 s of expiry), eviction on an upstream 401 is the same, the OBO cache keeps its 10 000-entry ceiling while the client-credentials one stays unbounded, and single-flight stays on the OBO path only.
Behavior change for existing configurations: an oauth2_token_exchange server whose identity provider answers slower than the server's timeout_ms now gets a 503 token_exchange_unavailable instead of waiting (preflight) or failing as an upstream connect error (tool call). Nothing to edit. No schema or startup-config change.
Tests: two new cases in mcp-token-exchange-obo-e2e. One points three servers with a 400 ms timeout_ms at a token endpoint that takes 3 s, and checks initialize, an MCP tool call and an OpenAPI tool call each answer 503 token_exchange_unavailable well inside the timeout, then that the abandoned exchange still finishes and serves the next request without a second exchange. The other runs the 401 → failed re-exchange sequence on an MCP and an OpenAPI server and reads the usage events off the SLS exporter: both carry a non-zero upstream latency, while a call whose very first exchange fails carries 0. Removing the deadline, either reached_upstream marking, or hard-coding the flag each turns the relevant case red. The cache refactor is covered by the existing OBO e2e and oauth2 client-credentials unit tests, plus direct unit tests of TokenCache (skew, lifetime clamp, bounded eviction, unbounded mode).
… re-exchange as dispatched
Three follow-ups to the Entra OBO token exchange:
- Every OBO exchange (the up-front one on `initialize` / `server/discover`
and the one on a tool call or tool list, for `type: mcp` and
`type: openapi`) is bounded by the server's `timeout_ms`, the same
deadline as its other upstream calls. Running out of it is a 503
`token_exchange_unavailable`. The shared exchange keeps running for the
other requests waiting on it.
- When the upstream answers 401 and the re-exchange fails, the tool call's
UsageEvent is recorded as dispatched (it reached the upstream), so it
keeps its upstream latency.
- The OBO and `oauth2` client-credentials token caches share one
implementation (`token_cache::TokenCache`); keys, TTL rule, capacity and
single-flight are unchanged on both paths.
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MCP and OpenAPI token operations now use request deadlines. OAuth and exchanged-token caching use a shared implementation. Token-exchange errors record whether upstream contact occurred, and usage events use that status. End-to-end tests cover delayed exchanges and failed re-exchanges.
A shared cache now handles token expiry, lifetime calculation, lookup, insertion, removal, and optional capacity cleanup. OAuth and exchanged-token caches use it.
TokenExchangeError wraps the failure and records whether it reached upstream. The gateway retains this metadata, and usage events set the dispatched status from it.
Deadlines for token and upstream operations crates/aisix-mcp/src/bridge.rs, crates/aisix-mcp/src/openapi.rs, crates/aisix-mcp/src/token_exchange.rs
MCP and OpenAPI paths pass deadlines to token acquisition. The same deadline bounds transport establishment, HTTP sending, and response-body reading.
End-to-end timeout and usage checks tests/e2e/src/cases/mcp-token-exchange-obo-e2e.test.ts
Tests cover delayed token exchanges, subsequent completion, and usage records for failed initial exchanges and failed re-exchanges after upstream contact.
sequenceDiagram
participant MCPBridge
participant OpenAPIExecutor
participant TokenExchangeAuth
participant TokenEndpoint
participant Upstream
participant UsageRecorder
MCPBridge->>TokenExchangeAuth: Request token with deadline
OpenAPIExecutor->>TokenExchangeAuth: Request token with deadline
TokenExchangeAuth->>TokenEndpoint: Exchange token
TokenEndpoint-->>TokenExchangeAuth: Return token or failure
TokenExchangeAuth-->>MCPBridge: Return token or timeout
TokenExchangeAuth-->>OpenAPIExecutor: Return token or timeout
OpenAPIExecutor->>Upstream: Send authenticated request
Upstream-->>OpenAPIExecutor: Return response
OpenAPIExecutor->>TokenExchangeAuth: Retry token exchange after upstream 401
TokenExchangeAuth->>TokenEndpoint: Exchange token
TokenEndpoint-->>TokenExchangeAuth: Return exchange failure
TokenExchangeAuth-->>OpenAPIExecutor: Return failure with upstream-contact status
OpenAPIExecutor->>UsageRecorder: Record dispatched status
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Possibly related PRs
api7/aisix#1361: This PR updates the OBO token-exchange implementation, failure metadata, and gateway state added there.
api7/aisix#1360: This PR sets dispatched status based on upstream contact, which affects whether usage events retain upstream latency.
Merge Risk: Moderate · previous review 95d3f
The timeout test does not reliably protect continued token exchange after a request gives up. Make it observe completion independently before merging.
Pre-merge checks: 5 · 1
Failed checks: 1 inconclusive
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Linked Issues check
Issue #1898 is open and directly linked. Its provided text contains no coding acceptance criteria. It refers to an external Feishu requirements document, which is not available in the review evidence.…
Provide the coding requirements from the referenced Feishu document, or another reviewable acceptance-criteria source, to compare them with the implementation.
Passed checks: 5 passed
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Description Check
Check skipped - CodeRabbit’s high-level summary is enabled.
Title check
The title clearly summarizes the two main changes: bounding OBO token exchange by the server timeout and recording failed re-exchanges as dispatched.
Out of Scope Changes check
The changed files support the stated Entra OBO objectives. Deadline propagation covers token exchange paths. Dispatch tracking fixes failed re-exchange events. The shared cache refactor preserves gran…
E2e Test Quality Review
PASS — The PR adds end-to-end coverage through the gateway, mock IdP, MCP upstream, OpenAPI REST upstream, and SLS exporter. Tests cover cached and per-caller exchanges, missing subjects, provider fai…
Security Check
No security vulnerability was introduced in the reviewed diff. - Category 1 — No issues found. Token values and caller credentials remain redacted in Debug implementations. New token-exchange logs inc…
Full details: Out of Scope Changes check
Explanation
The changed files support the stated Entra OBO objectives. Deadline propagation covers token exchange paths. Dispatch tracking fixes failed re-exchange events. The shared cache refactor preserves grant-specific behavior. The added tests cover these changes. No unrelated change is demonstrated.
Full details: E2e Test Quality Review
Explanation
PASS — The PR adds end-to-end coverage through the gateway, mock IdP, MCP upstream, OpenAPI REST upstream, and SLS exporter. Tests cover cached and per-caller exchanges, missing subjects, provider failures, upstream 401 re-exchange, timeout responses for MCP and OpenAPI paths, continuation of timed-out single-flight exchanges, and usage latency. Assertions use structured status, error-code, token, upstream, and log checks. The mocks model external dependencies that are not suitable for local E2E runs. The changed Rust paths also preserve lock-based cache access and check relevant errors.
Full details: Security Check
Explanation
No security vulnerability was introduced in the reviewed diff. - Category 1 — No issues found. Token values and caller credentials remain redacted in Debug implementations. New token-exchange logs include only the server identifier, status, and bounded transport error text. Token-exchange responses expose fixed failure messages. - Category 2 — No issues found. The change adds only in-process token caches. It adds no database persistence. - Category 3 — No issues found. The diff changes MCP token exchange, caching, and timeout handling. It adds no mutating endpoint or permission check. - Category 4 — No issues found. The diff adds no cross-resource lookup or ownership operation. - Category 5 — No issues found. The changed TLS client setup preserves configured certificate verification semantics. The new code does not invert TLS flags or lower TLS requirements. - Category 6 — No issues found. Separate process-global caches remain separate for OAuth client credentials and OBO exchange tokens. The OBO cache retains its capacity limit. - Category 7 — No issues found. The diff adds no configuration reference resolution path and does not introduce literal secret-reference use. The changed behavior is limited to deadline propagation, shared cache implementation, token-exchange error metadata, and usage attribution. No changed code logs, serializes, stores, or returns raw access tokens, client secrets, or authentication headers.
Full details: Linked Issues check
Explanation
Issue #1898 is open and directly linked. Its provided text contains no coding acceptance criteria. It refers to an external Feishu requirements document, which is not available in the review evidence. The PR summary shows Entra OBO timeout handling, dispatch tracking, shared caching, and tests, but complete compliance with the external requirements cannot be established.
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Provide the coding requirements from the referenced Feishu document, or another reviewable acceptance-criteria source, to compare them with the implementation.
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Actionable comments posted: 1
🪄 Fix comments: Fix CodeRabbit comments on this PR
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Inline comments:
Review comments at @tests/e2e/src/cases/mcp-token-exchange-obo-e2e.test.ts:
- Around line 653-656: Update the MCP OBO test’s readiness gate so it waits for
an independent signal that the original exchange populated the cache, rather
than issuing `/mcp/obohang` requests that can resume the abandoned flight. After
that signal, make one follow-up request and assert its response and the
token-endpoint hit count.
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Three follow-ups to the Entra On-Behalf-Of token exchange from #1361.
Fixes api7/AISIX-Cloud#1898
The exchange is now bounded by the server's
timeout_ms. Before, the exchangeinitialize/server/discoverruns up front on/mcp/{server}only had the token client's global 30 s cap, so a slow identity provider held the client's first request well past the timeout the operator configured. The exchange on a tool call had a related problem: it ran inside the connect (or, fortype: openapi, the tool-call) deadline, so running out of it surfaced as a generic upstream connect failure instead of the identity provider being unavailable. Every exchange site now uses the same per-server deadline as the server's other upstream calls (timeout_ms, 30 s when unset; the token endpoint client keeps its own 30 s request cap, so atimeout_msabove 30 s does not extend an exchange):initialize/server/discoverpreflight,type: mcpandtype: openapi: bounded bytimeout_msfrom when the preflight starts.type: mcptool call or tool list: the exchange shares one deadline with the connect that follows it. The credential is now obtained before the session is opened, against that deadline, so an exchange that runs out of it is reported as such. Theoauth2client-credentials mint on the same path keeps its existing "connect timed out" outcome.type: openapitool call: the call's deadline now bounds each network step on its own (credential, request, response body) instead of wrapping the whole call, for the same reason. A slow REST API is still "tool call timed out" as before.Running out of the deadline is a 503
token_exchange_unavailableon/mcp/{server}, like any other identity-provider unavailability; the aggregated/mcpkeeps absorbing it as that server's failure. Single-flight is unchanged: the exchange runs to completion in its own task, so a request that gives up does not cancel it, the other requests waiting on it get its outcome, and a token it obtains is cached for the next request.A failed re-exchange after an upstream 401 is recorded as dispatched. The usage event's
dispatchedflag means "this event describes work that reached an upstream", and it decides whether the event keeps its upstream latency and gets an upstream span. When the upstream rejected the exchanged token and the re-exchange then failed, the 503's tool-call event was recorded as not dispatched, so it showedupstream_latency_ms: 0even though the upstream had been contacted. The bridges now carry whether the failing exchange followed upstream contact (TokenExchangeError::reached_upstream), and the event follows it. A failure on the first exchange is still not dispatched.The two token caches share one implementation.
token_cache::TokenCacheholds the tokens for both the OBO exchange and theoauth2client-credentials grant. It is a pure refactor: each grant keeps its own key derivation and its own process-global instance, the TTL rule is the same (expires_incapped at 30 days, 3600 s when absent, not reused within 60 s of expiry), eviction on an upstream 401 is the same, the OBO cache keeps its 10 000-entry ceiling while the client-credentials one stays unbounded, and single-flight stays on the OBO path only.Behavior change for existing configurations: an
oauth2_token_exchangeserver whose identity provider answers slower than the server'stimeout_msnow gets a 503token_exchange_unavailableinstead of waiting (preflight) or failing as an upstream connect error (tool call). Nothing to edit. No schema or startup-config change.Tests: two new cases in
mcp-token-exchange-obo-e2e. One points three servers with a 400 mstimeout_msat a token endpoint that takes 3 s, and checksinitialize, an MCP tool call and an OpenAPI tool call each answer 503token_exchange_unavailablewell inside the timeout, then that the abandoned exchange still finishes and serves the next request without a second exchange. The other runs the 401 → failed re-exchange sequence on an MCP and an OpenAPI server and reads the usage events off the SLS exporter: both carry a non-zero upstream latency, while a call whose very first exchange fails carries 0. Removing the deadline, eitherreached_upstreammarking, or hard-coding the flag each turns the relevant case red. The cache refactor is covered by the existing OBO e2e andoauth2client-credentials unit tests, plus direct unit tests ofTokenCache(skew, lifetime clamp, bounded eviction, unbounded mode).🤖 Generated with Claude Code
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