fix(fastmcp): accept zone_url as valid audience in AuthProvider#123
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Keycard PKCE access tokens carry aud=zone_url rather than aud=resource_url (the MCP resource is indicated by a separate `resource` claim). The previous implementation set audience to only the MCP resource URL, causing token validation to fail with invalid_token for all Keycard-issued PKCE tokens. Fix: set audience to a list containing both the resource URL and zone_url, so the JWTVerifier accepts either form.
The grant() decorator built auth_info with resource_client_id set to self.client.config.client_id, which for WebIdentity is the DCR-registered ua:<hash> identifier. This changes on every restart and cannot be pre-registered as a Keycard application credential. Fix: when application_credential has an identity_manager (WebIdentity), use its stable key_id instead. This matches the identifier registered via keycard agent api application-credentials --type public-key.
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Problem
keycardai-fastmcp'sAuthProvidersetsself.audienceto the MCP resource URL (e.g.https://my-server.fly.dev/mcp). But Keycard PKCE access tokens haveaud = zone_url(e.g.https://abc123.keycard.cloud) — the actual MCP resource is in a separateresourceclaim, not inaud.This causes token validation to always fail with
invalid_token/ "audience mismatch" for any MCP server usingkeycardai-fastmcp'sAuthProviderwith PKCE-issued tokens.The older
keycardai-mcp-fastmcppackage works correctly because it usesAuthSettings.issuer_urlfor validation, which doesn't checkaudagainst the resource URL.Fix
Accept both
audforms by settingaudienceto a list:The
JWTVerifieralready handles list audiences by checkingaud in self.audience, so a token with eitheraud = resource_urloraud = zone_urlwill pass validation.Repro
Deploy any MCP server using
keycardai-fastmcp'sAuthProvider+WebIdentity, connect via Keycard PKCE, observeBearer token rejected: audience mismatchin server logs.🤖 Generated with Claude Code