Incoming request headers in passed to callbacks via RequestHandlerExtra<ServerRequest, ServerNotification>

[KKonstantinov]

Incoming Request headers passed down to callbacks via RequestHandlerExtra

Motivation and Context

An application often times needs access to the original request headers, for example, whenever it is sitting behind a reverse proxy, and the reverse proxy is setting some headers itself.

One practical example: A trace ID / correlation header is generated at the API gateway / reverse proxy later, then passed to the actual remote MCP server. The MCP server needs to utilize the traceparent to store it in logs, etc.

How Has This Been Tested?

SSE and Streamable transport - resources and tools.

Breaking Changes

No breaking changes.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

Additional context

Adding the headers as "requestHeaders" inside RequestHandlerExtra appears the appropriate place to put this, since it contributes to a non-breaking change.