Client ID Metadata Document

Support for the Client ID Metadata Document (draft-ietf-oauth-client-id-metadata-document <https://datatracker.ietf.org/doc/draft-ietf-oauth-client-id-metadata-document/>_) can be turned on via IDP_OIDC_CIMD_ENABLED.

When enabled, clients can use an HTTPS URL as their client_id. The authorization server will fetch the metadata document from that URL to obtain the client's registration information. No prior registration (such as Dynamic Client Registration) is required. CIMD clients are always public clients and must use PKCE.

The fetched metadata is cached for the duration specified by IDP_OIDC_CIMD_CACHE_TIMEOUT (default: 3600 seconds). Rate limiting and a per-client_id lock prevent excessive outbound fetches.

To restrict which URLs are accepted as a client_id, override the is_cimd_url_allowed() adapter method.