modelcontextprotocol / modelcontextprotocol/php-sdk
[Client][Auth] SEP-2468: Validate iss parameter in authorization response (RFC 9207)
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- PHP
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Description
Implements SEP-2468 for the MCP Spec 2026-07-28 release.
Tracked by umbrella #338.
Spec summary
Requires MCP authorization responses to include an explicit
iss(issuer) parameter per RFC 9207. Clients MUST validateissagainst the AS that initiated the flow to mitigate authorization mix-up attacks in multi-IdP environments.
PHP SDK changes
- When handling the authorization-code redirect, the client must validate the returned
issmatches the AS that produced theauthorization_endpointURL. - Required for any multi-AS scenario; cross-cuts with #319 (Auth Code + PKCE) but filed separately because the validation logic crosses callback + AS-metadata state.
- Server-side: N/A — MCP servers are resource servers, not authorization servers;
issis emitted by the AS.
Related
- Umbrella #338
- Sub-task / depends on: #319 (Auth Code + PKCE foundation)
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start with the client’s authorization-code redirect handling and the AS-metadata state that produced the authorization_endpoint URL. Review the Auth Code + PKCE foundation in #319 and the requirements in RFC 9207; done means validating the returned iss against the initiating authorization server, including multi-AS flows.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- php
- Domain
- authentication, security
- Issue type
- Feature
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Quiet
- Clarity
- Mostly clear
- Newbie friendliness
- 52/100