cloudflare/workers-oauth-provider
feat: support private_key_jwt for CIMD clients
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#264 geöffnet am 29.07.2026
enhancementgood first issue
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Beschreibung
Summary
Support private_key_jwt client authentication for clients identified by a Client ID Metadata Document.
Current behavior
CIMD support accepts only token_endpoint_auth_method: "none". Documents that advertise both none and private_key_jwt can work because the provider selects none, but a client that requires private_key_jwt cannot complete authorization code exchange.
This is not a core MCP compliance blocker because the MCP specification makes private_key_jwt optional. It is useful for clients that want stronger authentication than an unauthenticated public client.
Acceptance criteria
- Parse and validate the client's
jwksorjwks_urimetadata according to the CIMD draft. - Authenticate token endpoint requests using
private_key_jwt. - Validate assertion issuer, subject, audience, signature, expiration, and unique identifier/replay constraints.
- Apply SSRF protections to remotely fetched JWKS documents.
- Advertise
private_key_jwtonly when the complete token-endpoint path is supported. - Add positive and negative tests for key rotation, invalid audience, expiry, replay, unknown keys, malformed assertions, and SSRF-sensitive URLs.
- Document how this interacts with the
global_fetch_strictly_publiccompatibility flag.