MCP TypeScript client SDK: HTTP client transports and OAuth requests followed cross-origin redirects and re-sent custom headers and request bodies
### Summary
In affected versions, the SDK's HTTP client transports and OAuth requests followed redirects to any origin.
If an MCP server or authorization server redirected a request to another origin, that origin received custom request headers (such as an `X-API-Key` set in `requestInit.headers`) and the `mcp-session-id` header. On a `307` or `308` it also received the request body, including OAuth token requests with their `refresh_token` and `client_secret`.
On current runtimes `fetch` already drops the `Authorization` header across origins.
### Am I affected?
Yes, if your application uses `StreamableHTTPClientTransport`, `SSEClientTran
MCP TypeScript SDK: OAuth client could send credentials to an authorization server chosen by the MCP server
MCP TypeScript SDK is the official TypeScript SDK for Model Context Protocol servers and clients. Starting in version 1.12.0 and prior to versions 1.31.0 and 2.2.0, the SDK's OAuth client support let the MCP server a client connected to decide which authorization server received the client's OAuth credentials. Stored and pre-provisioned credentials were not bound to the authorization server they belong to. A malicious or compromised MCP server could name its own authorization server in its protected resource metadata. Without any user interaction, the client would send that server the `refresh_token` and `client_secret` stored from an earlier