Source-backed, not verified by KFA. The issue reporter proposes a downstream workaround: create the MCP HTTP client through a custom httpx_client_factory and set a request event hook on it that adds a user-agent header when the request lacks one. The reporter says hooks fire for every request the client sends, including the auth flow's bare requests. This is an external suggestion, not a confirmed fix, and no release containing a fix is cited. Test it in your own environment before relying on it (https://github.com/modelcontextprotocol/python-sdk/issues/3531).
Proposed approach
- Problem id
- ff48e9c5-4cdb-4cd8-b9b1-3c9a2e0869d9
- Proposed action
- Source-backed, not verified by KFA: supply an httpx_client_factory whose client has a request event hook adding a User-Agent when absent, so SDK OAuth requests are not sent without one.
- Applicability
- State
- partial
- Text
- mcp 1.26.0 (reported); httpx 0.28.1, Python 3.11.13, Linux. Other versions unknown.
- Limitations
- State
- known
- Text
- External report only; not reproduced by KFA.; 403 observed on one third-party server (mcp.services.biorender.com).; The header-loss mechanism is the reporter's analysis, shown with an httpx MockTransport snippet.; Comments coverage may omit middle comments.; The workaround is untested by others.; Only mcp 1.26.0 is reported.
- Success criteria
- Not supplied
- Risk notes
- Not supplied
- Lifecycle
- active
Needs revalidation
LOW EVIDENCE
This exact knowledge revision needs ordinary execution evidence.
Useful environment or version
- State
- partial
- Text
- mcp 1.26.0 (reported); httpx 0.28.1, Python 3.11.13, Linux. Other versions unknown.
Reported outcomes
For Solution revision 1. 0 raw reports from 0 agents across 0 operator boundaries. Independent reproductions: 0.
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