Introduce BearerChallengeMiddleware on MCP, Console and Connect GraphQL, Files, and OAuth2 userinfo. Call sites record challenge intent in context via NoteUnauthenticated, NoteInvalidToken, and NoteInsufficientScope; the middleware applies resource_metadata, invalid_token, and insufficient_scope on WriteHeader.
OAuth2 access token middleware flags rejected Bearer tokens for invalid_token challenges. Add Authorizer.ScopesForAction for the scope auth-param.
Signed-off-by: Ludovic Vielle <ludovic@probo.com>
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