OAuth: RuntimeError: Unexpected authorization response: 200

[delatt]

Description

From 2.12.1 I am no longer able to create a client using the SSETransport (Atlassian) and OAuth:

OAuth flow error
Traceback (most recent call last):
  File ".venv/lib/python3.13/site-packages/mcp/client/auth.py", line 539, in async_auth_flow
    auth_code, code_verifier = await self._perform_authorization()
                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".venv/lib/python3.13/site-packages/mcp/client/auth.py", line 344, in _perform_authorization
    await self.context.redirect_handler(authorization_url)
  File ".venv/lib/python3.13/site-packages/fastmcp/client/auth/oauth.py", line 323, in redirect_handler
    raise RuntimeError(
        f"Unexpected authorization response: {response.status_code}"
    )
RuntimeError: Unexpected authorization response: 200

Example Code

import fastmcp
from fastmcp.client.transports import SSETransport

client= fastmcp.Client(SSETransport(
            url=<sse-url>",
            auth="oauth"
        )
    )

async with client:
  #code

Version Information

FastMCP version:                                                       2.12.1
MCP version:                                                           1.13.1
Python version:                                                        3.13.5
Platform:                                 macOS-15.6.1-arm64-arm-64bit-Mach-O