Set OIDC application_type on Dynamic Client Registration per SEP-837#408
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koic wants to merge 1 commit into
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Set OIDC application_type on Dynamic Client Registration per SEP-837#408koic wants to merge 1 commit into
application_type on Dynamic Client Registration per SEP-837#408koic wants to merge 1 commit into
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## Motivation and Context SEP-837 (modelcontextprotocol/modelcontextprotocol#837, merged for the 2026-07-28 spec release) updates the authorization spec to require MCP clients to specify an appropriate OIDC `application_type` (`"native"` vs `"web"`) during Dynamic Client Registration, so the authorization server can apply the matching redirect URI policy and native and web clients do not collide on redirect URI validation rules. This mirrors the approach taken by the TypeScript SDK (typescript-sdk#2266) and the Python SDK (python-sdk#2784): - `MCP::Client::OAuth::Discovery.infer_application_type(redirect_uris)` returns `"native"` when every redirect URI is a native-app URI (a custom non-http(s) scheme per RFC 8252 Section 7.1, or an http(s) URI with a loopback host per RFC 8252 Section 7.3) and `"web"` otherwise, including for nil, empty, or unparseable input. Loopback detection reuses the existing `loopback_host?` helper, so lookalike hosts such as `localhost.example.com` or `127.attacker.com` are not treated as native. - `Flow#ensure_client_registered` now posts the metadata through the new `registration_client_metadata` helper, which merges the inferred `application_type` into the DCR request body only when the user did not set one explicitly (symbol or string key); an explicit value always wins. Resolves modelcontextprotocol#375. ## How Has This Been Tested? New tests in `test/mcp/client/oauth/discovery_test.rb` cover the inference: loopback http URIs (IPv4, IPv6, `localhost`), custom schemes, https URIs, mixed lists, the `localhost.example.com` lookalike, nil/empty input, and unparseable URIs. New tests in `test/mcp/client/oauth/flow_test.rb` assert on the actual DCR request body via WebMock `assert_requested`: loopback redirect URI registers `"application_type": "native"`, an HTTPS redirect URI registers `"web"`, and an explicit `application_type` (symbol- or string-keyed) is never overridden. ## Breaking Changes None. The DCR request body gains an `application_type` member only when the user has not specified one; RFC 7591 requires authorization servers to accept and use known metadata fields, and OIDC-registration servers already default this field to `"web"` when absent.
atesgoral
approved these changes
Jun 14, 2026
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Motivation and Context
SEP-837 (modelcontextprotocol/modelcontextprotocol#837, merged for the 2026-07-28 spec release) updates the authorization spec to require MCP clients to specify an appropriate OIDC
application_type("native"vs"web") during Dynamic Client Registration, so the authorization server can apply the matching redirect URI policy and native and web clients do not collide on redirect URI validation rules.This mirrors the approach taken by the TypeScript SDK (typescript-sdk#2266) and the Python SDK (python-sdk#2784):
MCP::Client::OAuth::Discovery.infer_application_type(redirect_uris)returns"native"when every redirect URI is a native-app URI (a custom non-http(s) scheme per RFC 8252 Section 7.1, or an http(s) URI with a loopback host per RFC 8252 Section 7.3) and"web"otherwise, including for nil, empty, or unparseable input. Loopback detection reuses the existingloopback_host?helper, so lookalike hosts such aslocalhost.example.comor127.attacker.comare not treated as native.Flow#ensure_client_registerednow posts the metadata through the newregistration_client_metadatahelper, which merges the inferredapplication_typeinto the DCR request body only when the user did not set one explicitly (symbol or string key); an explicit value always wins.Resolves #375.
How Has This Been Tested?
New tests in
test/mcp/client/oauth/discovery_test.rbcover the inference: loopback http URIs (IPv4, IPv6,localhost), custom schemes, https URIs, mixed lists, thelocalhost.example.comlookalike, nil/empty input, and unparseable URIs.New tests in
test/mcp/client/oauth/flow_test.rbassert on the actual DCR request body via WebMockassert_requested: loopback redirect URI registers"application_type": "native", an HTTPS redirect URI registers"web", and an explicitapplication_type(symbol- or string-keyed) is never overridden.Breaking Changes
None. The DCR request body gains an
application_typemember only when the user has not specified one; RFC 7591 requires authorization servers to accept and use known metadata fields, and OIDC-registration servers already default this field to"web"when absent.Types of changes
Checklist