MCP session id is required

[Yeffri1]

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Discussion Topic

Hello,

I am attempting to use an AI tool (like ChatGPT or another Model Context Protocol client) to interact with a service running on an ngrok tunnel. However, the client is consistently failing to authenticate, and the server is rejecting the request.

The Error:
The server returns the following JSON response to the initial request:

{"error":{"code":-32000,"message":"Bad Request: Mcp-Session-Id header is required"},"id":"","jsonrpc":"2.0"}

[Starlight143]

One mental model that helps here is to separate three layers:

1. transport/session requirements
2. authentication
3. authorization

Mcp-Session-Id is not really the same thing as auth. It is part of how the server correlates the protocol conversation and state across requests.

So even if the bearer token or API auth is correct, the request can still fail if the transport/session contract is incomplete.

In practice, I think servers should make this easier to debug by being explicit about:

• when a session id must first be created
• whether the client is expected to persist and replay it
• whether a new auth token can continue an existing session
• whether session state is tied to a single principal

The most dangerous failure mode is when session state and auth state get mixed together implicitly. That tends to create brittle integrations and confusing authorization bugs later.