Failed to register MCP tools | HTTP 400: Bad Request

[dbudym-cs]

Summary

MCP Gateway v0.2.4: tools/list returns HTTP 400 for Atlassian MCP HTTP.
The issue #19652 was closed but the problem still persists.

Environment

Component	Version
gh-aw	v0.63.1
MCP Gateway	v0.2.4
Backend	Atlassian MCP Server (Streamable HTTP transport)
Endpoint	https://mcp.atlassian.com/v1/mcp

Steps to Reproduce

1. Configure an HTTP-based MCP backend (Atlassian MCP Server):

   mcp-servers:
     atlassian:
       url: https://mcp.atlassian.com/v1/mcp
       headers:
         Authorization: Basic ${{ secrets.ATLASSIAN_BASIC_AUTH_BASE64 }}
       allowed: ["*"]

Run a workflow that uses the Atlassian MCP backend

Attempting connection (timeout: 10s)...
✓ atlassian: connected
⏱️  TIMING: Server check for atlassian took 80ms

[2026-03-25T12:21:00Z] [DEBUG] [backend] GetOrLaunch called for server: atlassian
[2026-03-25T12:21:00Z] [INFO] [backend] Configuring HTTP MCP backend: atlassian, url=https://mcp.atlassian.com/v1/mcp
[2026-03-25T12:21:00Z] [INFO] [backend] Successfully configured HTTP MCP backend: atlassian
[2026-03-25T12:21:01Z] [WARN] [backend] Failed to register tools from atlassian (took 538.570177ms): backend error listing tools: code=-32603, message=HTTP 400: Bad Request

Expected Behavior
tools/list should succeed and return the available tools from the Atlassian MCP server.

Actual Behavior
tools/list fails with HTTP 400: Bad Request

[lpcox]

Tracking issue created in gh-aw-mcpg: https://github.com/github/gh-aw-mcpg/issues/github/gh-aw-mcpg#2607

The root cause identified is that NewHTTPConnection bypasses the SDK's Streamable HTTP transport when custom headers (like Authorization) are present, falling back to a plain JSON-RPC-over-POST path that sends "params": null and skips the required MCP initialize handshake. The fix is to pass custom headers through the SDK transport via a custom http.RoundTripper.

Generated by Gateway Issue Dispatcher · ◷

[lpcox]

Closing — this was fixed in MCP Gateway commit 10c82c8 ("Fix HTTP 400 on tools/list for Atlassian MCP: inject custom headers via RoundTripper in SDK transports"). The tracking issue github/gh-aw-mcpg#2607 is also closed.

Root cause: When custom headers (e.g. Authorization) were configured, NewHTTPConnection bypassed the SDK's Streamable HTTP transport and fell back to a plain JSON-RPC path that sent params: null and skipped the MCP initialize handshake.

Fix: Custom headers are now injected via a headerInjectingRoundTripper so the SDK's StreamableClientTransport is used regardless of whether authentication headers are present. This has been shipping since MCP Gateway v0.2.5+.