bug: OAuth uses wrong authorization URL and missing redirectUri config

[christso]

Problem

MCP OAuth fails with enterprise auth servers (Keycloak, Azure AD, Okta) due to two issues:

1. Wrong authorization URL (SDK bug)

MCP SDK 1.15.1 incorrectly constructs the authorization URL by appending /authorize to the issuer URL instead of using authorization_endpoint from OAuth metadata.

# Expected (from .well-known/openid-configuration):
https://idp.example.com/realms/mcp/protocol/openid-connect/auth

# Actual (SDK 1.15.1):
https://idp.example.com/authorize

This causes the browser to redirect to a non-existent endpoint.

2. No redirect URI configuration

OAuth servers validate that the redirect URI exactly matches a pre-registered URI. OpenCode hardcodes http://127.0.0.1:19876/mcp/oauth/callback, which may not be registered on the OAuth server.

Users cannot configure a custom redirect URI to match what's registered (e.g., Claude Code's http://localhost:41842/callback).

Reproduction Steps

KeyCloak

1. Configure an MCP server with OAuth in opencode.json:

   "mcp": {
     "example-mcp-server": {
       "type": "remote",
       "url": "https://your-mcp-server.com",
       "oauth": {
         "clientId": "your-client-id",
         "scope": "openid profile email"
       }
     }
   }
   

2. Run the auth command:

   opencode mcp auth example-mcp-server
   

3. Browser opens and navigates to the authorization URL

4. Result: "Page not found" error because the SDK constructs the wrong URL (/authorize instead of the actual authorization_endpoint from OAuth discovery)

GitHub MCP

I observed similar behaviour with GitHub MCP.

1. Create an OpenCode OAuth app in Developer settings

2. Add GitHub MCP to .config/opencode.json:

   {
     "$schema": "https://opencode.ai/config.json",
     "mcp": {
       "github": {
         "type": "remote",
         "url": "https://api.githubcopilot.com/mcp/",
         "enabled": true,
         "oauth": {
           "clientId": "your-client-id",
           "clientSecret": "your-client-secret"
         }
       }
     }
   }
   

3. Run the auth command:

   opencode mcp auth github
   

4. Result: The SDK constructs the wrong URL (/authorize instead of the actual authorization_endpoint from OAuth discovery). Note: The URL github.com/authorize actually points to the github user "authorize".

Solution

1. Upgrade MCP SDK to 1.25.1+ which correctly reads authorization_endpoint
2. Add redirectUri config so users can specify the callback URL

User Configuration

This is a typical configuration for KeyCloak that impersonates Claude Code:

"mcp": {
  "<server-name>": {
    "type": "remote",
    "url": "https://<your-mcp-server>",
    "oauth": {
      "clientId": "f637990b-e806-402b-9652-2eac0ae05840",
      "redirectUri": "http://localhost:41842/callback",
      "scope": "openid profile email"
    }
  }
}

Explanation

1. If I upgrade MCP SDK from 1.15.1 to 1.25.1+, it constructs the correct path for KeyCloak.

2. The MCP SDK upgrade will also fix GitHub MCP OAuth because it will resolve to the correct URL: github.com/login/oauth/authorize.

2. However, KeyCloak also validates the callback URL (currently many enterprise systems match the callback URL pattern for VS Code and Claude Code, not Open Code). If I set the redirectUri to impersonate Claude Code, the authentication is successful.

[github-actions[bot]]

This issue might be a duplicate of existing issues. Please check:

• #5444: MCP with oauth doesn't work (same root cause - Dynamic Client Registration failures with enterprise OAuth servers like Jira)
• #5716: Is github mcp serve with oauth supposed to be working? (DCR HTTP 422 failure with GitHub MCP)
• #5665: Support multiple authentication flows for enterprise SSO compatibility (related authentication flow enhancement)
• #5748: Proposal: Provider Auth v2 (related auth infrastructure improvements)

Feel free to ignore if your specific case involves different requirements.

[christso]

@thdxr Could you please relabel this as a bug? The root causes are identified: SDK uses wrong authorization URL + missing redirectUri config. PR #5940 has the fix.

[rekram1-node]

@christso when you opened the issue you made it as a feature request instead of a bug report so it wasn't labled as a bug