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fix(pier): MCP 401 challenge names only resource_metadata

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- drop the response-writer wrapper that appended scope="read" to every 401
- the SDK handler now gets the original writer; RequireBearerToken still sets no Scopes
- TestPierTracerSmoke pins the exact challenge for a bad and a missing bearer
- README and docs/services/mcp.md describe the header without a scope parameter
This commit is contained in:
Jakub Zych
2026-11-06 15:09:10 +01:00
parent ef47baf0a1
commit 609caa4f3f
4 changed files with 33 additions and 46 deletions
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docs/services/mcp.md
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@@ -138,7 +138,7 @@ Sessions follow the streamable HTTP transport: `initialize` opens one, `Mcp-Sess
## Protected resource metadata
pier serves the OAuth protected resource metadata (RFC 9728) at `/.well-known/oauth-protected-resource` and at `/.well-known/oauth-protected-resource<mcp.path>`: the resource, the authorization server (the verifier's resource origin, else `app.url`), the supported scopes and the bearer method. When the published verifier implements `pact.MCPAdvertisedScopes` and `pact.MCPAdvertisedScopes.MCPScopesSupported` is non-empty, that slice is copied; otherwise the document keeps `pier.PRMScopes` (`read`, `write`, `ai`, `offline_access`, `backend`). pier does not read `pact.MemberTokenScopeCatalog`. The list the OAuth server plugin publishes is the MCP advertised set: the fixed names `read`, `write`, `ai`, `offline_access` and `backend` are always on it. Declared member scopes follow the plugin's `golem15.oauthserver.mcp_scopes` filter, which is that plugin's key and not a framework `mcp.*` key: unset means every declared member scope, a set filter means only those declared names, and an empty filter means the five fixed names only. An empty `wristband.Options.ScopesSupported` on the MCP flavour resolves to those five names; a non-empty list is used as given. OpenID Connect discovery stays `openid`, `profile` and `email`. A route reads who called a tool with `pact.MCPCallFrom`. A 401 carries `WWW-Authenticate: Bearer resource_metadata="…", scope="read"`, which is how a client finds the authorization server. `mcp.resource` must equal the resource the OAuth server issues tokens for; a difference is logged as a warning at boot.
pier serves the OAuth protected resource metadata (RFC 9728) at `/.well-known/oauth-protected-resource` and at `/.well-known/oauth-protected-resource<mcp.path>`: the resource, the authorization server (the verifier's resource origin, else `app.url`), the supported scopes and the bearer method. When the published verifier implements `pact.MCPAdvertisedScopes` and `pact.MCPAdvertisedScopes.MCPScopesSupported` is non-empty, that slice is copied; otherwise the document keeps `pier.PRMScopes` (`read`, `write`, `ai`, `offline_access`, `backend`). pier does not read `pact.MemberTokenScopeCatalog`. The list the OAuth server plugin publishes is the MCP advertised set: the fixed names `read`, `write`, `ai`, `offline_access` and `backend` are always on it. Declared member scopes follow the plugin's `golem15.oauthserver.mcp_scopes` filter, which is that plugin's key and not a framework `mcp.*` key: unset means every declared member scope, a set filter means only those declared names, and an empty filter means the five fixed names only. An empty `wristband.Options.ScopesSupported` on the MCP flavour resolves to those five names; a non-empty list is used as given. OpenID Connect discovery stays `openid`, `profile` and `email`. A route reads who called a tool with `pact.MCPCallFrom`. A 401 carries `WWW-Authenticate: Bearer resource_metadata="…"`, which is how a client finds the authorization server. It carries no scope parameter, so a client requests the scopes listed in the metadata document and consent decides what is granted. `mcp.resource` must equal the resource the OAuth server issues tokens for; a difference is logged as a warning at boot.
## Security notes