Token handler drops RFC 8707 resource on refresh_token (and authorization_code) grants; provider can't see it #3720

Initial Checks

• I confirm that I'm using the newest release of my line (checked on v2.3.0)
• I confirm that I searched for my issue in https://github.com/modelcontextprotocol/python-sdk/issues before opening this issue

Release line

2.x (current stable)

Description

The token handler parses the RFC 8707 resource parameter on a refresh_token grant but never passes it to the provider, and OAuthAuthorizationServerProvider.exchange_refresh_token has no way to receive it.

• RefreshTokenRequest declares resource (handlers/token.py#L36-L45).
• The refresh branch calls self.provider.exchange_refresh_token(client_info, refresh_token, scopes) and drops token_request.resource (L238).
• exchange_refresh_token(self, client, refresh_token, scopes) has no resource parameter (provider.py#L259-L264).
• The JWT bearer branch does forward it (resource=token_request.resource, L268).

So an authorization server built on the SDK can't apply RFC 8707 §2.2 on refresh ("such policy may limit the acceptable resources to those that were originally granted by the resource owner or a subset thereof") or answer a mismatched resource with invalid_target. The MCP authorization spec requires clients to send resource in token requests, so the value is always there; the provider just can't see it. #3447 added RefreshToken.resource so the granted resource can be stored, but there is still nothing to compare it with.

The same applies to the authorization_code grant: the handler doesn't compare token_request.resource with AuthorizationCode.resource and doesn't pass it to exchange_authorization_code (L200), so a mismatch is accepted silently.

For comparison, the TypeScript SDK's token handler passes resource to exchangeRefreshToken and to the authorization code exchange.

Today the only workaround is to subclass TokenHandler and hand the form value to the provider out of band.

Expected: the provider can see the requested resource on both grants. One backwards-compatible option is an optional resource: str | None = None argument on exchange_refresh_token and exchange_authorization_code (or a params object, as the JWT bearer path does). Optionally, the handler could itself return invalid_target when resource is sent and differs from refresh_token.resource / auth_code.resource.

Example Code

class Provider(OAuthAuthorizationServerProvider[AuthorizationCode, RefreshToken, AccessToken]):
    async def exchange_refresh_token(
        self, client: OAuthClientInformationFull, refresh_token: RefreshToken, scopes: list[str]
    ) -> OAuthToken:
        # POST /token
        #   grant_type=refresh_token&refresh_token=...&resource=https://other.example/mcp
        # The requested resource is not available here, so the provider can't refuse it
        # with invalid_target or check it against refresh_token.resource.
        ...

Python & MCP Python SDK

Python 3.12.12
mcp v2.3.0