fix(mcp): match the MCP host by full authority; keep legacy API keys off the OAuth token prefix

Author: waleedlatif1

apps/sim/lib/api-key/crypto.test.ts

@@ -10,7 +10,10 @@
  */
 import { randomBytes } from 'crypto'
 import { resetEnvMock, setEnv } from '@sim/testing'
-import { afterAll, beforeAll, beforeEach, describe, expect, it } from 'vitest'
+import { afterAll, beforeAll, beforeEach, describe, expect, it, vi } from 'vitest'
+
+const { mockGenerateSecureToken } = vi.hoisted(() => ({ mockGenerateSecureToken: vi.fn() }))
+vi.mock('@sim/security/tokens', () => ({ generateSecureToken: mockGenerateSecureToken }))
 
 beforeAll(() => {
   setEnv({ API_ENCRYPTION_KEY: undefined })
@@ -21,6 +24,7 @@ afterAll(resetEnvMock)
 import {
   decryptApiKey,
   encryptApiKey,
+  generateApiKey,
   hashApiKey,
   isEncryptedApiKeyFormat,
   isLegacyApiKeyFormat,
@@ -86,3 +90,11 @@ describe('api-key format helpers', () => {
     expect(isEncryptedApiKeyFormat('sim_abc')).toBe(false)
   })
 })
+
+describe('generateApiKey', () => {
+  it('never issues a legacy key that reads as an OAuth access token', () => {
+    mockGenerateSecureToken.mockReturnValueOnce('oat_collision').mockReturnValueOnce('plain_token')
+    expect(generateApiKey()).toBe('sim_plain_token')
+    expect(mockGenerateSecureToken).toHaveBeenCalledTimes(2)
+  })
+})

apps/sim/lib/api-key/crypto.ts

@@ -3,6 +3,7 @@ import { decrypt, encrypt } from '@sim/security/encryption'
 import { sha256Hex } from '@sim/security/hash'
 import { generateSecureToken } from '@sim/security/tokens'
 import { toError } from '@sim/utils/errors'
+import { OAUTH_ACCESS_TOKEN_PREFIX } from '@/lib/auth/oauth-provider'
 import { env } from '@/lib/core/config/env'
 
 const logger = createLogger('ApiKeyCrypto')
@@ -60,10 +61,17 @@ export async function decryptApiKey(encryptedValue: string): Promise<{ decrypted
 
 /**
  * Generates a standardized API key with the 'sim_' prefix (legacy format)
+ *
+ * Never one starting with the OAuth access-token prefix: base64url can spell
+ * `sim_oat_`, and a bearer credential's prefix is what tells an OAuth token
+ * from an API key.
  * @returns A new API key string
  */
 export function generateApiKey(): string {
-  return `sim_${generateSecureToken(24)}`
+  for (;;) {
+    const key = `sim_${generateSecureToken(24)}`
+    if (!key.startsWith(OAUTH_ACCESS_TOKEN_PREFIX)) return key
+  }
 }
 
 /**

apps/sim/lib/api/mcp/host-routing.test.ts

@@ -61,6 +61,13 @@ describe('Sim MCP host routing', () => {
       }
     )
 
+    it('tells the MCP host from an app on the same hostname but another port', () => {
+      mocks.mcpUrl = 'http://localhost:3001/mcp'
+      expect(resolveSimMcpHostPath('localhost:3000', '/workspace')).toBeNull()
+      expect(resolveSimMcpHostPath('localhost:3001', '/mcp')).toBe('/api/mcp')
+      expect(resolveSimMcpHostPath('localhost:3001', '/workspace')).toBe('not_found')
+    })
+
     it('serves the app host as before, without a second MCP URL', () => {
       expect(resolveSimMcpHostPath('sim.ai', '/mcp')).toBeNull()
       expect(resolveSimMcpHostPath('sim.ai', '/workspace')).toBeNull()

apps/sim/lib/api/mcp/host-routing.ts

@@ -4,9 +4,16 @@ import { getBaseUrl } from '@/lib/core/utils/urls'
 const PROTECTED_RESOURCE_METADATA = '/.well-known/oauth-protected-resource'
 const AUTHORIZATION_SERVER_METADATA = '/.well-known/oauth-authorization-server'
 
-/** A `Host` header's hostname: lower-cased, without port or the trailing root dot. */
-function hostnameOf(host: string): string {
-  return host.toLowerCase().replace(/:\d+$/, '').replace(/\.$/, '')
+/**
+ * A `Host` header as a URL authority under `protocol`: lower-cased, without the
+ * trailing root dot, and without the scheme's default port, so it compares
+ * equal to `URL.host`. `null` when the header is not a valid authority.
+ */
+function authorityOf(host: string, protocol: string): string | null {
+  const normalized = host.replace(/\.(?=:\d+$|$)/, '')
+  return URL.canParse(`${protocol}//${normalized}`)
+    ? new URL(`${protocol}//${normalized}`).host
+    : null
 }
 
 /**
@@ -30,7 +37,7 @@ export function resolveSimMcpHostPath(
   const mcp = new URL(getSimMcpUrl())
   const dedicated = mcp.origin !== new URL(getBaseUrl()).origin
   const internalMetadataPath = `${PROTECTED_RESOURCE_METADATA}${SIM_MCP_ROUTE_PATH}`
-  if (!host || hostnameOf(host) !== mcp.hostname) {
+  if (!host || authorityOf(host, mcp.protocol) !== mcp.host) {
     return dedicated && (pathname === SIM_MCP_ROUTE_PATH || pathname === internalMetadataPath)
       ? 'not_found'
       : null