Constant PROTECTED_RESOURCE_METADATA_PATH 

pub(crate) const PROTECTED_RESOURCE_METADATA_PATH: &str = "/.well-known/oauth-protected-resource";

The well-known path served by this module.

Per RFC 9728 §3 this is the OAuth 2.0 Protected Resource Metadata well-known URI; MCP clients probe it as a fallback when no resource_metadata parameter is present in a 401’s WWW-Authenticate.