MCP-AUT-003

PRM resource equals the canonical server URI

“The resource parameter MUST identify the MCP server that the client intends to use the token with, using the canonical URI as defined in RFC 8707 Section 2.” — spec anchor

How to fix this

Set `resource` in the Protected Resource Metadata to this server's canonical URI (RFC 8707 §2). It is the audience every token will be minted for, so a wrong value produces tokens your server should reject.

Example: failing and passing

The metadata's resource names api.example.com, but the client is talking to https://mcp.example.com/mcp, so under RFC 9728 the client must discard this metadata.

Violates MCP-AUT-003 · JSON

{
  "resource": "https://api.example.com/mcp",
  "authorization_servers": ["https://auth.example.com"]
}

The resource value is the MCP server's own canonical URI, the URL the client sends its requests to.

Complies with MCP-AUT-003 · JSON

{
  "resource": "https://mcp.example.com/mcp",
  "authorization_servers": ["https://auth.example.com"]
}

How the validator checks this

Probe P8.2, against a streamable-http server on the modern protocol. What it reports:

pass: resource matches the probed server URI (…)
fail: Protected Resource Metadata has no `resource` field — the client has no canonical URI to request a token for

Quoted from the probe that runs this check, so it cannot drift from what the validator actually reports.

This rule is checked deterministically: a fail here is a certain violation, not an inference.

Checked in the same request as MCP-AUT-002, MCP-AUT-009.

Check your own server against MCP-AUT-003

Probe P8.2 checks MCP-AUT-003 in the same request as 2 other rules, so one run shows your server's result for this rule next to the rest. Validate a server or read how the validator works.

Background on this topic: how to add OAuth to an MCP server.

Other Authorization rules

MCP-AUT-001Unauthenticated request returns 401 with WWW-Authenticate resource_metadata
MCP-AUT-002RFC 9728 Protected Resource Metadata is served and valid
MCP-AUT-004Each listed authorization server exposes RFC 8414 or OIDC discovery metadata
MCP-AUT-005AS advertises authorization_response_iss_parameter_supported: true
MCP-AUT-006WWW-Authenticate includes a scope parameter
MCP-AUT-007Insufficient scope returns 403 with error="insufficient_scope"
MCP-AUT-008Tokens with a foreign audience are rejected
MCP-AUT-009offline_access absent from scopes_supported / challenge scope
MCP-AUT-010AS advertises S256 in code_challenge_methods_supported
MCP-AUT-011AS supports Client ID Metadata Documents, not DCR alone