fix(mcp): bound OAuth callback steps and log each phase to pinpoint hangs

The MCP OAuth callback could hang indefinitely after burning state, with no
error, no timeout, and no log — the request stalls somewhere between the burn
and token persistence with no observable I/O. Wrap each awaited callback step
(loadPreregisteredClient, mcpAuthGuarded, clearVerifier, discoverServerTools)
with a per-step timeout so a stalled operation surfaces as a labeled error
instead of hanging forever, and log start/done for every step, every guarded
OAuth fetch phase (validate/request/read-body), and the token-exchange DB
writes. The last start without a matching done names the exact stall point.

Author: waleedlatif1

apps/sim/app/api/mcp/oauth/callback/route.ts

@@ -25,6 +25,46 @@ const logger = createLogger('McpOauthCallbackAPI')
 
 export const dynamic = 'force-dynamic'
 
+class OauthCallbackStepTimeout extends Error {
+  constructor(step: string, ms: number) {
+    super(`MCP OAuth callback step "${step}" did not settle within ${ms}ms`)
+    this.name = 'OauthCallbackStepTimeout'
+  }
+}
+
+/**
+ * Times and bounds one awaited step of the callback so a stalled operation
+ * surfaces as a labeled, logged error instead of hanging the request forever.
+ * The losing promise is not cancelled (a wedged DB/socket op can't be), so it
+ * settles in the background with its rejection swallowed; the point is that the
+ * request stops waiting on it and the logs name the exact step that stalled.
+ */
+async function timedStep<T>(step: string, ms: number, fn: () => Promise<T>): Promise<T> {
+  const start = Date.now()
+  logger.info(`OAuth callback step start: ${step}`)
+  const work = fn()
+  work.catch(() => {})
+  let timer: ReturnType<typeof setTimeout> | undefined
+  try {
+    const value = await Promise.race([
+      work,
+      new Promise<never>((_, reject) => {
+        timer = setTimeout(() => reject(new OauthCallbackStepTimeout(step, ms)), ms)
+        timer.unref?.()
+      }),
+    ])
+    logger.info(`OAuth callback step done: ${step} (${Date.now() - start}ms)`)
+    return value
+  } catch (error) {
+    logger.error(`OAuth callback step failed: ${step} (${Date.now() - start}ms)`, {
+      error: toError(error).message,
+    })
+    throw error
+  } finally {
+    clearTimeout(timer)
+  }
+}
+
 function escapeHtml(value: string): string {
   return value
     .replace(/&/g, '&amp;')
@@ -145,8 +185,9 @@ export const GET = withRouteHandler(async (request: NextRequest) => {
         serverId
       )
     }
+    const serverUrl = server.url
     try {
-      assertSafeOauthServerUrl(server.url)
+      assertSafeOauthServerUrl(serverUrl)
     } catch {
       return respond(
         'MCP OAuth requires https (or http://localhost for development).',
@@ -157,16 +198,22 @@ export const GET = withRouteHandler(async (request: NextRequest) => {
     }
 
     // Burn state before token exchange so a replayed callback cannot reuse it.
-    await clearState(row.id, 'callback:burn-before-exchange')
+    await timedStep('clearState(burn)', 10_000, () =>
+      clearState(row.id, 'callback:burn-before-exchange')
+    )
 
-    const preregistered = await loadPreregisteredClient(server.id)
+    const preregistered = await timedStep('loadPreregisteredClient', 15_000, () =>
+      loadPreregisteredClient(server.id)
+    )
     const provider = new SimMcpOauthProvider({ row, preregistered })
     let result: Awaited<ReturnType<typeof mcpAuthGuarded>>
     try {
-      result = await mcpAuthGuarded(provider, {
-        serverUrl: server.url,
-        authorizationCode: code,
-      })
+      result = await timedStep('mcpAuthGuarded', 60_000, () =>
+        mcpAuthGuarded(provider, {
+          serverUrl,
+          authorizationCode: code,
+        })
+      )
     } catch (e) {
       logger.error('Token exchange failed during MCP OAuth callback', e)
       return respond(
@@ -176,7 +223,11 @@ export const GET = withRouteHandler(async (request: NextRequest) => {
         server.id
       )
     } finally {
-      await clearVerifier(row.id)
+      await timedStep('clearVerifier', 10_000, () => clearVerifier(row.id)).catch((e) =>
+        logger.error('Failed to clear PKCE verifier after MCP OAuth callback', {
+          error: toError(e).message,
+        })
+      )
     }
 
     if (result !== 'AUTHORIZED') {
@@ -185,7 +236,9 @@ export const GET = withRouteHandler(async (request: NextRequest) => {
 
     try {
       // forceRefresh: skip any stale cache from before re-auth.
-      await mcpService.discoverServerTools(session.user.id, server.id, server.workspaceId, true)
+      await timedStep('discoverServerTools', 30_000, () =>
+        mcpService.discoverServerTools(session.user.id, server.id, server.workspaceId, true)
+      )
     } catch (e) {
       logger.warn('Post-auth tools refresh failed', toError(e).message)
     }

apps/sim/lib/mcp/oauth/storage.ts

@@ -170,18 +170,22 @@ export async function saveClientInformation(
   info: OAuthClientInformationMixed
 ): Promise<void> {
   const encrypted = await encryptClientInformation(info)
+  logger.info('Persisting MCP OAuth client information', { rowId })
   await db
     .update(mcpServerOauth)
     .set({ clientInformation: encrypted, updatedAt: new Date() })
     .where(eq(mcpServerOauth.id, rowId))
+  logger.info('Persisted MCP OAuth client information', { rowId })
 }
 
 export async function saveTokens(rowId: string, tokens: OAuthTokens): Promise<void> {
   const encrypted = await encryptTokens(tokens)
+  logger.info('Persisting MCP OAuth tokens', { rowId })
   await db
     .update(mcpServerOauth)
     .set({ tokens: encrypted, lastRefreshedAt: new Date(), updatedAt: new Date() })
     .where(eq(mcpServerOauth.id, rowId))
+  logger.info('Persisted MCP OAuth tokens', { rowId })
 }
 
 export async function saveCodeVerifier(rowId: string, verifier: string): Promise<void> {

apps/sim/lib/mcp/pinned-fetch.ts

@@ -1,9 +1,12 @@
 import type { FetchLike } from '@modelcontextprotocol/sdk/shared/transport.js'
+import { createLogger } from '@sim/logger'
 import type { Agent } from 'undici'
 import { createPinnedFetchWithDispatcher } from '@/lib/core/security/input-validation.server'
 import { validateMcpServerSsrf } from '@/lib/mcp/domain-check'
 import { McpError } from '@/lib/mcp/types'
 
+const logger = createLogger('McpOauthFetch')
+
 /** Pinned fetch for the live MCP transport, plus a handle to release its sockets. */
 export interface PinnedMcpFetch {
   fetch: typeof fetch
@@ -151,13 +154,17 @@ function releaseStreamOnSettle(
 export function createSsrfGuardedMcpFetch(timeoutMs: number = OAUTH_FETCH_TIMEOUT_MS): FetchLike {
   return (async (url, init) => {
     const target = typeof url === 'string' ? url : url.href
+    const host = URL.canParse(target) ? new URL(target).host : target
+    const startedAt = Date.now()
     const timeoutSignal = AbortSignal.timeout(timeoutMs)
     // Bound every phase — validation, request, body read — by the deadline + caller signal.
     const signal = init?.signal ? AbortSignal.any([init.signal, timeoutSignal]) : timeoutSignal
     // Per-request Agent must be torn down (finally): a one-shot leg never reuses its socket.
     let dispatcher: Agent | undefined
     try {
+      logger.info('OAuth guarded fetch: validating', { host })
       const resolvedIP = await withDeadline(validateMcpServerSsrf(target), signal)
+      logger.info('OAuth guarded fetch: requesting', { host, resolvedIP: resolvedIP ?? 'unpinned' })
       let response: Response
       if (resolvedIP) {
         const pinned = createPinnedFetchWithDispatcher(resolvedIP, {
@@ -175,11 +182,23 @@ export function createSsrfGuardedMcpFetch(timeoutMs: number = OAUTH_FETCH_TIMEOU
       if (contentType.includes('text/event-stream')) {
         const streamed = releaseStreamOnSettle(response, dispatcher, signal)
         dispatcher = undefined // teardown ownership moved to releaseStreamOnSettle
+        logger.info('OAuth guarded fetch: streaming response', {
+          host,
+          status: response.status,
+          ms: Date.now() - startedAt,
+        })
         return streamed
       }
-      return await bufferUnderDeadline(response, signal)
+      logger.info('OAuth guarded fetch: reading body', { host, status: response.status })
+      const buffered = await bufferUnderDeadline(response, signal)
+      logger.info('OAuth guarded fetch: done', {
+        host,
+        status: response.status,
+        ms: Date.now() - startedAt,
+      })
+      return buffered
     } catch (error) {
-      const host = URL.canParse(target) ? new URL(target).host : target
+      logger.warn('OAuth guarded fetch: failed', { host, ms: Date.now() - startedAt })
       // Relabel only our own deadline — by reason identity, not signal state (which may
       // abort independently just after the deadline).
       if (timeoutSignal.aborted && error === timeoutSignal.reason) {