PRM Missing hindering - no metadata for OAuth discovery

[clgtm]

Hi Guys, looks like PRM is missing, is this by design?

Command:   authprobe scan --llm-max-tokens=1080 --openai-api-key="***REDACTED***" http://localhost:8004/mcp
Scanning:  http://localhost:8004/mcp
Scan time: Feb 21, 2026 01:04:44 UTC
Github:    https://github.com/authprobe/authprobe

Funnel
  [1] MCP probe (401 + WWW-Authenticate)      [-] SKIP
        auth not required

  [2] MCP initialize + tools/list             [+] PASS
        initialize -> 200
        notifications/initialized -> 202
        tools/list -> 200 (tools: perplexity_ask, perplexity_research,
        perplexity_reason, perplexity_search)

  [3] PRM fetch matrix                        [X] FAIL
        PRM unreachable or unusable; OAuth discovery unavailable

  [4] Auth server metadata                    [-] SKIP
        auth not required

  [5] Token endpoint readiness (heuristics)   [-] SKIP
        auth not required

  [6] Dynamic client registration (RFC 7591)  [-] SKIP
        auth not required

┌───────────────────────┤ CALL TRACE ├───────────────────────┐
Call Trace Using: https://github.com/authprobe/authprobe

  ┌────────────┐                                                    ┌────────────┐    
  │ authprobe  │                                                    │ MCP Server │    
  └─────┬──────┘                                                    └─────┬──────┘    
        │                                                                 │           
        │ ╔═══ Step 1: MCP probe                    ═══════╪═══════════════════╗
        │  GET http://localhost:8004/mcp                                 
        │  Reason: 401 + WWW-Authenticate discovery                      
        │    Accept:  text/event-stream
        │    Host:    localhost:8004
        ├─────────────────────────────────────────────────────────────────►│
        │  200 OK                                                        
        │    Access-Control-Expose-Headers:  Mcp-Session-Id,mcp-protocol-version
        │    Cache-Control:                  no-cache, no-transform
        │    Connection:                     keep-alive
        │    Content-Type:                   text/event-stream
        │    Date:                           Sat, 21 Feb 2026 01:04:36 GMT
        │    Vary:                           Origin
        │    X-Powered-By:                   Express
        │◄─────────────────────────────────────────────────────────────────┤
        │                                                                  │
        │ ╔═══ Step 2: MCP initialize               ═══════╪═══════════════════╗
        │  POST http://localhost:8004/mcp                                
        │  Reason: Step 2: MCP initialize + tools/list (pre-init tools/list)
        │    Accept:                application/json, text/event-stream
        │    Content-Type:          application/json
        │    Host:                  localhost:8004
        │    Mcp-Protocol-Version:  2025-11-25
        ├─────────────────────────────────────────────────────────────────►│
        │  200 OK                                                        
        │    Access-Control-Expose-Headers:  Mcp-Session-Id,mcp-protocol-version
        │    Connection:                     keep-alive
        │    Content-Length:                 7432
        │    Content-Type:                   application/json
        │    Date:                           Sat, 21 Feb 2026 01:04:44 GMT
        │    Keep-Alive:                     timeout=5
        │    Vary:                           Origin
        │    X-Powered-By:                   Express
        │◄─────────────────────────────────────────────────────────────────┤
        │                                                                  │
        │  POST http://localhost:8004/mcp                                
        │  Reason: Step 2: MCP initialize + tools/list (initialize)      
        │    Accept:                application/json, text/event-stream
        │    Content-Type:          application/json
        │    Host:                  localhost:8004
        │    Mcp-Protocol-Version:  2025-11-25
        ├─────────────────────────────────────────────────────────────────►│
        │  200 OK                                                        
        │    Access-Control-Expose-Headers:  Mcp-Session-Id,mcp-protocol-version
        │    Connection:                     keep-alive
        │    Content-Length:                 813
        │    Content-Type:                   application/json
        │    Date:                           Sat, 21 Feb 2026 01:04:44 GMT
        │    Keep-Alive:                     timeout=5
        │    Vary:                           Origin
        │    X-Powered-By:                   Express
        │◄─────────────────────────────────────────────────────────────────┤
        │                                                                  │
        │  POST http://localhost:8004/mcp                                
        │  Reason: Step 2: MCP initialize + tools/list (notifications/initialized)
        │    Accept:                application/json, text/event-stream
        │    Content-Type:          application/json
        │    Host:                  localhost:8004
        │    Mcp-Protocol-Version:  2025-11-25
        ├─────────────────────────────────────────────────────────────────►│
        │  202 Accepted                                                  
        │    Access-Control-Expose-Headers:  Mcp-Session-Id,mcp-protocol-version
        │    Connection:                     keep-alive
        │    Content-Type:                   text/plain; charset=UTF-8
        │    Date:                           Sat, 21 Feb 2026 01:04:44 GMT
        │    Keep-Alive:                     timeout=5
        │    Vary:                           Origin
        │    X-Powered-By:                   Express
        │◄─────────────────────────────────────────────────────────────────┤
        │                                                                  │
        │  POST http://localhost:8004/mcp                                
        │  Reason: Step 2: MCP initialize + tools/list (null id probe)   
        │    Accept:                application/json, text/event-stream
        │    Content-Type:          application/json
        │    Host:                  localhost:8004
        │    Mcp-Protocol-Version:  2025-11-25
        ├─────────────────────────────────────────────────────────────────►│
        │  400 Bad Request                                               
        │    Access-Control-Expose-Headers:  Mcp-Session-Id,mcp-protocol-version
        │    Connection:                     keep-alive
        │    Content-Length:                 101
        │    Content-Type:                   application/json
        │    Date:                           Sat, 21 Feb 2026 01:04:44 GMT
        │    Keep-Alive:                     timeout=5
        │    Vary:                           Origin
        │    X-Powered-By:                   Express
        │◄─────────────────────────────────────────────────────────────────┤
        │                                                                  │
        │  POST http://localhost:8004/mcp                                
        │  Reason: Step 2: MCP initialize + tools/list (notification id probe)
        │    Accept:                application/json, text/event-stream
        │    Content-Type:          application/json
        │    Host:                  localhost:8004
        │    Mcp-Protocol-Version:  2025-11-25
        ├─────────────────────────────────────────────────────────────────►│
        │  200 OK                                                        
        │    Access-Control-Expose-Headers:  Mcp-Session-Id,mcp-protocol-version
        │    Connection:                     keep-alive
        │    Content-Length:                 78
        │    Content-Type:                   application/json
        │    Date:                           Sat, 21 Feb 2026 01:04:44 GMT
        │    Keep-Alive:                     timeout=5
        │    Vary:                           Origin
        │    X-Powered-By:                   Express
        │◄─────────────────────────────────────────────────────────────────┤
        │                                                                  │
        │  POST http://localhost:8004/mcp                                
        │  Reason: Step 2: MCP initialize + tools/list (origin probe)    
        │    Accept:                application/json, text/event-stream
        │    Content-Type:          application/json
        │    Host:                  localhost:8004
        │    Mcp-Protocol-Version:  2025-11-25
        │    Origin:                http://invalid.example
        ├─────────────────────────────────────────────────────────────────►│
        │  200 OK                                                        
        │    Access-Control-Allow-Origin:    http://invalid.example
        │    Access-Control-Expose-Headers:  Mcp-Session-Id,mcp-protocol-version
        │    Connection:                     keep-alive
        │    Content-Length:                 7433
        │    Content-Type:                   application/json
        │    Date:                           Sat, 21 Feb 2026 01:04:44 GMT
        │    Keep-Alive:                     timeout=5
        │    Vary:                           Origin
        │    X-Powered-By:                   Express
        │◄─────────────────────────────────────────────────────────────────┤
        │                                                                  │
        │  POST http://localhost:8004/mcp                                
        │  Reason: Step 2: MCP initialize + tools/list (protocol version probe)
        │    Accept:                application/json, text/event-stream
        │    Content-Type:          application/json
        │    Host:                  localhost:8004
        │    Mcp-Protocol-Version:  invalid
        ├─────────────────────────────────────────────────────────────────►│
        │  400 Bad Request                                               
        │    Access-Control-Expose-Headers:  Mcp-Session-Id,mcp-protocol-version
        │    Connection:                     keep-alive
        │    Content-Length:                 195
        │    Content-Type:                   application/json
        │    Date:                           Sat, 21 Feb 2026 01:04:44 GMT
        │    Keep-Alive:                     timeout=5
        │    Vary:                           Origin
        │    X-Powered-By:                   Express
        │◄─────────────────────────────────────────────────────────────────┤
        │                                                                  │
        │  POST http://localhost:8004/mcp                                
        │  Reason: Step 2: MCP initialize + tools/list (tools/list)      
        │    Accept:                application/json, text/event-stream
        │    Content-Type:          application/json
        │    Host:                  localhost:8004
        │    Mcp-Protocol-Version:  2025-11-25
        ├─────────────────────────────────────────────────────────────────►│
        │  200 OK                                                        
        │    Access-Control-Expose-Headers:  Mcp-Session-Id,mcp-protocol-version
        │    Connection:                     keep-alive
        │    Content-Length:                 7432
        │    Content-Type:                   application/json
        │    Date:                           Sat, 21 Feb 2026 01:04:44 GMT
        │    Keep-Alive:                     timeout=5
        │    Vary:                           Origin
        │    X-Powered-By:                   Express
        │◄─────────────────────────────────────────────────────────────────┤
        ▼                                                                  ▼

┌──────────────────┤ ROOT-CAUSE ANALYSIS ├───────────────────┐
The AuthProbe scan results highlight two main compliance issues with the MCP OAuth server implementation at http://localhost:8004/mcp, specifically in the context of MCP 2025-11-25 and related RFCs (RFC 9728, RFC 8414, JSON-RPC 2.0). Below is a detailed, spec-grounded analysis explaining why the failure is valid and justified, along with recommendations for corrective actions.

---

Summary of Findings

1. Failure at Step [3]: PRM fetch matrix

• Issue: PRM (Protected Resource Metadata) is unreachable or unusable.
• OAuth Discovery: OAuth-related discovery metadata is unavailable from the MCP endpoint.
• Implication: Without OAuth discovery metadata, clients cannot perform necessary dynamic discovery of the authorization server endpoints as required by RFC 8414.
• Validation: This failure is valid and justified because the MCP mode (even with "best-effort") expects reachable OAuth discovery endpoints to support authorization and token issuance properly.

2. Info: MCP_INITIALIZE_ORDERING_NOT_ENFORCED

• Evidence: A tools/list request returned 200 prior to initialize.
• Spec Reference: The MCP 2025-11-25 specification requires that the client MUST send an initialize request before any other MCP method calls (e.g., tools/list) to ensure proper session initialization.
• Impact: Serving MCP JSON-RPC methods before initialize is a protocol violation and leads to undefined or unsupported server/client state.
• Recommendation: The server MUST enforce ordering by rejecting all MCP JSON-RPC requests other than initialize with appropriate error responses (likely JSON-RPC error code -32000 or a custom error indicating "Not Initialized").

3. Low confidence: MCP_ORIGIN_NOT_VALIDATED

• Evidence: Origin header probes returned 200 instead of 403 or denial.
• Spec Reference: MCP 2025-11-25 recommends validating the Origin HTTP header to mitigate DNS rebinding attacks and cross-site request forgery.
• Requirement: Servers should return HTTP 403 Forbidden if the Origin header is invalid or unauthorized.
• Current Behavior: Server allows requests regardless of Origin.
• Impact: This leaves the server vulnerable to security issues related to cross-origin attacks.
• Recommendation: Implement strict Origin validation as per MCP recommendations. Reject unauthorized origins with HTTP 403.

---

Spec-Grounded Explanation and Correct Server Behavior

MCP Initialization Ordering (MCP 2025-11-25, Section 6.x)

• MCP protocol requires that clients MUST first issue the initialize method call before any other MCP JSON-RPC methods.
• Server MUST reject non-initialize requests if the session is not initialized.
• Correct behavior: Return a JSON-RPC error response with a clear error code/message indicating that initialization is required.

PRM Fetch Matrix and OAuth Discovery (RFC 8414, RFC 9728)

• MCP leverages OAuth 2.0 and requires dynamic discovery of authorization server endpoints (token, authorization, introspection).
• RFC 8414 defines the .well-known/oauth-authorization-server metadata endpoint essential for client discovery.
• Failure to serve this endpoint or the PRM matrix means clients cannot perform OAuth flows.
• MCP servers enforcing OAuth must provide this metadata discoverable and reachable.
• Correct behavior: Provide a reachable and standards-compliant OAuth authorization server metadata endpoint as per RFC 8414 at a standard location.

OAuth Token Endpoint Readiness (RFC 9728)

• Token endpoints and OAuth flows are essential for client authentication and authorization.
• Even in best-effort mode, minimal OAuth support must be accessible to support token issuance.
• The failure to reach the PRM matrix and OAuth discovery logically entails the token endpoint readiness step also fails or is skipped.
• Correct behavior: Ensure token endpoint adheres to RFC 9728, supports OAuth grant types, and is accessible according to OAuth discovery metadata.

Origin Validation (MCP 2025-11-25 Security Considerations)

• Origin validation mitigates DNS rebinding and CSRF vulnerabilities.
• Servers should check the Origin (and potentially Referer) headers on incoming requests.
• Invalid or unauthorized origins must be denied with HTTP 403.
• This prevents attackers from performing requests from malicious contexts.
• Correct behavior: Implement strict origin validation policy as described.

---

JSON-RPC 2.0 Handling (JSON-RPC 2.0 Specification)

• MCP interfaces are JSON-RPC 2.0 compliant.
• Responses must use standard JSON-RPC format with:
  • A top-level jsonrpc string "2.0"
  • method
  • id
  • For errors, an error object containing code, message, and optionally a data field.
• MCP servers must respond with JSON-RPC errors for requests violating protocol, e.g., requests before initialize.
• The server must not respond with HTTP 200 if the JSON-RPC request is invalid; the response body must carry JSON-RPC error indicating the failure mode.

---

Recommendations to Achieve Compliance and Pass AuthProbe

Issue	Required Action	Spec Reference
PRM fetch matrix unavailable	Implement OAuth discovery metadata endpoint at standard location (.well-known/oauth-authorization-server)	RFC 8414, MCP 2025-11-25
Initialize ordering not enforced	Enforce initialize as first MCP method; reject others with JSON-RPC error	MCP 2025-11-25, JSON-RPC 2.0
Origin not validated	Validate Origin header; return 403 for unauthorized origins	MCP 2025-11-25 Security

[kesku]

This server doesn't implement OAuth (it's API-key-based, as described in the README for setup). The PRM endpoint and OAuth discovery flow aren't applicable here since there's no authorization server to discover.

The initialize ordering and origin validation notes are good callouts though, thank you! We may look into those separately, but closing this issue based on title/main point.

[clgtm]

The initialize ordering and origin validation notes are good callouts though, thank you! We may look into those separately, but closing this issue based on title/main point.

Lack of session management (on initialize) hinders running multiple instances of mcp server, especially in scale-to-n (think enterprise deployments).

It would take a wrapper or some infra gymnastics to scale-out, not too difficult but you are essentially adding custom logic which ideally should reside with the mcp server.