Add support for initial access tokens in OAuth 2.0 Dynamic Client Registration #575

Summary

The MCP Inspector currently does not support initial access tokens when performing OAuth 2.0 Dynamic Client Registration (DCR), which limits its ability to work with authorization servers that require authentication for client registration.

Problem

According to RFC 7591 (OAuth 2.0 Dynamic Client Registration Protocol), authorization servers may optionally require an initial access token to authorize client registration requests. The MCP Inspector's current implementation only supports open registration (no authentication required).

Current Behavior

• Dynamic client registration works only with authorization servers that allow open registration
• No way to provide an initial access token during the registration process
• Registration fails with authorization servers that require pre-authorization

Expected Behavior

• Support for providing an initial access token during dynamic client registration
• Ability to register with protected client registration endpoints
• Support for both open and protected registration scenarios
• Environment variable support for secure token configuration

Use Case

Many production OAuth 2.0 authorization servers implement protected dynamic client registration for security reasons. This is especially common in:

• Enterprise environments
• Financial services (Open Banking)
• Healthcare systems
• CI/CD pipelines and automated deployments
• Any environment requiring strict client management

Technical Details

RFC 7591 Specification

According to RFC 7591, Section 1.2:

"Initial Access Token: OAuth 2.0 access token optionally issued by an authorization server to a developer or client and used to authorize calls to the client registration endpoint."

The token should be sent in the Authorization header:

POST /register HTTP/1.1
Authorization: Bearer <initial_access_token>
Content-Type: application/json

Current Implementation

In client/src/lib/oauth-state-machine.ts, the registration step calls:

const fullInformation = await registerClient(context.serverUrl, {
  metadata,
  clientMetadata,
});

Proposed Solution

1. Environment Variable Support: Add support for MCP_OAUTH_INITIAL_ACCESS_TOKEN environment variable
2. UI Configuration: Add an optional initial access token field to the client configuration UI
3. Priority Logic: Environment variable takes precedence over UI input for security
4. Update the OAuth state machine to include the token in registration requests
5. Modify the registerClient call to support the initial access token parameter
6. Update the MCP SDK if necessary to support this parameter

Configuration Methods (in order of priority)

1. Environment Variable: MCP_OAUTH_INITIAL_ACCESS_TOKEN=your_token_here
2. UI Input: Optional field in the OAuth configuration section
3. Config File: Include in inspector configuration (if applicable)

Additional Context

This enhancement would make MCP Inspector compatible with a broader range of OAuth 2.0 authorization servers and enable usage in:

• Enterprise environments that require protected client registration
• CI/CD pipelines where UI input is not feasible
• Automated deployments and testing scenarios
• Containerized environments where configuration via environment variables is standard

References

• RFC 7591: OAuth 2.0 Dynamic Client Registration Protocol
• OpenID Connect Dynamic Client Registration 1.0
• 12-Factor App Config - Best practices for configuration via environment variables