Support Client ID Metadata Documents in OAuth client
## Motivation and Context The MCP 2025-11-25 authorization specification and `draft-ietf-oauth-client-id-metadata-document-00` define Client ID Metadata Documents (CIMD): a client publishes its OAuth metadata at an HTTPS URL and uses that URL as the OAuth `client_id` instead of going through Dynamic Client Registration. The Python and TypeScript SDKs already implement this; the Ruby SDK now reaches parity. The change adds: - `MCP::Client::OAuth::Provider` accepts an optional `client_id_metadata_document_url:` keyword. - A new `Discovery.client_id_metadata_document_url?` validator enforces structural requirements. Spec-required: `https` scheme, a non-root path, and no fragment, userinfo, or `.`/`..` segments (including the percent-encoded form `%2E`). Stricter than the draft as an SDK policy: query strings are also rejected, because different encodings of the same query would yield distinct `client_id` strings for the same logical document. The loopback `http` carve-out used for discovery URLs does not extend to CIMD URLs, since the value is sent verbatim to the authorization server as the OAuth `client_id` and travels off-loopback. Validation failures raise `Provider::InvalidClientIDMetadataDocumentURLError`. - `Flow#ensure_client_registered` routes through CIMD only when the authorization server advertises `client_id_metadata_document_supported` as JSON `boolean true`; truthy non-boolean values (string `"true"`, `"false"`, etc.) fall back to DCR, matching the gating in the Python and TypeScript SDKs. - The CIMD `client_id` is NOT persisted to storage. AS support is re-read on every flow so a server that later drops CIMD support stops receiving the stale URL. Pre-registered `client_information` continues to win over CIMD when both are available. - `Flow#refresh!` reconstructs the CIMD `client_id` from live AS metadata when refreshing tokens obtained via CIMD. When support has been withdrawn and no other identity is stored, it raises a clear `AuthorizationError` rather than sending a `client_id` the authorization server no longer recognises. - The Provider docstring and README OAuth section explain that DCR `client_metadata` and the JSON document served at the CIMD URL are separate artifacts: DCR metadata MUST NOT include `client_id`, while the CIMD document MUST include `client_id` set to the URL, `client_name`, and `redirect_uris` covering `redirect_uri`. - `auth/basic-cimd` is removed from `conformance/expected_failures.yml`. ## How Has This Been Tested? `Discovery` tests cover: https with path accepted; non-https rejected (http, ftp, file); root and empty path rejected; fragment, query, and userinfo rejected; dot segments rejected including the percent-encoded form `%2E`; nil, empty, and malformed inputs rejected. `Provider` tests cover: the default `nil`; rejection of http URLs (loopback included); non-https schemes; root and empty path; fragment; query; userinfo; and dot segments. `Flow#run!` tests cover: skip DCR when the authorization server advertises CIMD and the provider has a URL; fall back to DCR when the authorization server does not advertise support; fall back to DCR when the value is the string `"false"` or `"true"`; pre-registered `client_information` wins over CIMD; the CIMD `client_id` is not persisted to storage; a second flow against an authorization server that has dropped CIMD support recovers via DCR. `Flow#refresh!` tests cover: refresh reconstructs the CIMD `client_id` without a stored `client_information`; refresh raises when the authorization server no longer advertises CIMD support; stored `client_information` takes precedence over the CIMD URL during refresh. Conformance: `auth/basic-cimd` now passes 12/12 with no warnings. `bundle exec rake test`, `bundle exec rake rubocop`, and `bundle exec rake conformance` are all green. ## Breaking Changes None. The `client_id_metadata_document_url:` keyword is purely opt-in and defaults to `nil`. When the keyword is omitted, the DCR flow is unchanged. Existing OAuth users see no behaviour change. The CIMD path is only entered when both the user explicitly configures a URL and the authorization server advertises support via `client_id_metadata_document_supported: true`.
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Koichi ITO
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1 changed files with 727 additions and 7 deletions
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@ -367,6 +367,68 @@ module MCP
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refute(Discovery.secure_url?("not a url"))
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end
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def test_client_id_metadata_document_url_accepts_https_with_path
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assert(Discovery.client_id_metadata_document_url?("https://app.example.com/client-metadata.json"))
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assert(Discovery.client_id_metadata_document_url?("https://app.example.com/path/to/cm"))
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assert(Discovery.client_id_metadata_document_url?("https://app.example.com:8443/cm"))
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end
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def test_client_id_metadata_document_url_accepts_boundary_forms
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# An uppercase scheme is `https` after case folding (URIs are scheme-insensitive, RFC 3986 Section 3.1).
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assert(Discovery.client_id_metadata_document_url?("HTTPS://app.example.com/cm"))
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# A trailing slash and consecutive slashes are non-root, non-dot paths.
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# RFC 3986 `remove_dot_segments` does not collapse them, so they remain
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# stable `client_id` strings rather than aliasing another URL.
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assert(Discovery.client_id_metadata_document_url?("https://app.example.com/cm/"))
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assert(Discovery.client_id_metadata_document_url?("https://app.example.com//cm"))
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# The default https port is equivalent to omitting it; either form is a valid origin.
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assert(Discovery.client_id_metadata_document_url?("https://app.example.com:443/cm"))
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# IPv6 literal hosts and Punycode (IDN) hosts are ordinary hosts.
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assert(Discovery.client_id_metadata_document_url?("https://[2001:db8::1]/cm"))
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assert(Discovery.client_id_metadata_document_url?("https://[::1]/cm"))
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assert(Discovery.client_id_metadata_document_url?("https://xn--e1afmkfd.example.com/cm"))
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end
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def test_client_id_metadata_document_url_rejects_non_https_schemes
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refute(Discovery.client_id_metadata_document_url?("http://localhost/cm"))
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refute(Discovery.client_id_metadata_document_url?("http://app.example.com/cm"))
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refute(Discovery.client_id_metadata_document_url?("ftp://app.example.com/cm"))
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refute(Discovery.client_id_metadata_document_url?("file:///cm"))
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end
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def test_client_id_metadata_document_url_rejects_root_and_empty_path
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refute(Discovery.client_id_metadata_document_url?("https://app.example.com"))
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refute(Discovery.client_id_metadata_document_url?("https://app.example.com/"))
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end
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def test_client_id_metadata_document_url_rejects_fragment_query_userinfo
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refute(Discovery.client_id_metadata_document_url?("https://app.example.com/cm#frag"))
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refute(Discovery.client_id_metadata_document_url?("https://app.example.com/cm?x=1"))
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refute(Discovery.client_id_metadata_document_url?("https://user:pass@app.example.com/cm"))
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refute(Discovery.client_id_metadata_document_url?("https://user@app.example.com/cm"))
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end
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def test_client_id_metadata_document_url_rejects_dot_segments
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refute(Discovery.client_id_metadata_document_url?("https://app.example.com/./cm"))
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refute(Discovery.client_id_metadata_document_url?("https://app.example.com/a/../cm"))
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refute(Discovery.client_id_metadata_document_url?("https://app.example.com/cm/."))
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refute(Discovery.client_id_metadata_document_url?("https://app.example.com/cm/.."))
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# Percent-encoded `.` would otherwise let `%2E` and `.` produce
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# different `client_id` values for the same document.
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refute(Discovery.client_id_metadata_document_url?("https://app.example.com/%2E/cm"))
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refute(Discovery.client_id_metadata_document_url?("https://app.example.com/%2e/cm"))
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end
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def test_client_id_metadata_document_url_rejects_nil_or_empty_or_malformed
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refute(Discovery.client_id_metadata_document_url?(nil))
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refute(Discovery.client_id_metadata_document_url?(""))
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refute(Discovery.client_id_metadata_document_url?("not a url"))
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refute(Discovery.client_id_metadata_document_url?("https://"))
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end
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def test_resource_covers_blocks_percent_encoded_dot_segment_bypass
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server = Discovery.canonicalize_url("https://srv.example.com/api/%2e%2e/mcp")
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prm = Discovery.canonicalize_url("https://srv.example.com/api")
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