Feature request: HTTP Stream transport with per-request credential injection

[fjprobos]

Problem

The server currently only supports stdio transport, which requires a separate process per user and hardcoded credentials at startup. This makes it impossible to deploy a single shared instance that multiple users can connect to with their own Metabase credentials.

Proposed Solution

Add support for HTTP Stream transport (MCP_TRANSPORT=http) where:

1. The server starts an HTTP endpoint instead of reading from stdio
2. Each request provides Metabase credentials via headers:
   • x-metabase-url — Metabase instance URL
   • x-metabase-api-key — API key (or x-metabase-username + x-metabase-password)
3. A MetabaseClient is created per session and attached via FastMCP's authenticate() hook
4. All tools resolve the client from the request context via getClient(ctx)

This enables a single deployed instance to serve multiple teams/users pointing at different Metabase instances — ideal for cloud/SaaS deployments.

Additional

Also includes a legacy sse-server.js wrapper for clients that only support the older SSE transport (spawns stdio processes per connection).

A pull request with a working implementation is available: https://github.com/fjprobos/metabase-mcp-server/pull/new/feat/http-stream-transport-with-per-request-auth