SSLV3_ALERT_HANDSHAKE_FAILURE when using private gateway

[OS-anasantos]

Initial Checks

• I confirm that I'm using the latest version of MCP Python SDK
• I confirm that I searched for my issue in https://github.com/modelcontextprotocol/python-sdk/issues before opening this issue

Description

I'm calling an MCP "https://mcp.deepwiki.com/mcp" through a private gateway. Because of that, the URL I'm calling is "https://secure-gateway:8081", so far so good, but unfortunately, I get _"ConnectError('[SSL: SSLV3_ALERT_HANDSHAKE_FAILURE] sslv3 alert handshake failure (ssl.c:1000)')".

Unfortunately, in _handle_post_request, even if I send the headers "X-Forwarded-Host", they are ignored. It seems that "sni_hostname" is only retrieved by using extensions which are not present here.

Is this expected, or is this an issue?

Example Code

Python & MCP Python SDK

Python: 3.12
MCP Python: 1.16.0

[maxisbey]

Related PRs that should hopefully fix this:

• Add streamable_http_client which accepts httpx.AsyncClient instead of httpx_client_factory #1177
• Add support to custom extensions in streamable http client #1479