GitHub connections issue from TeamCity server through proxy when using libcurl 4.8.0

Symptoms

Following an upgrade to TeamCity version 2024.12.3, issues arose when connecting to GitHub repositories using certain authentication methods. Connections using user/password or token-based authentication methods fail, while connections using SSH deploy keys function correctly. The issue only appears when the connections need to be routed through a proxy, and some of them seem to be ignored. Setting the proxy settings on TeamCity and letting it propagate the settings to git doesn't work, while configuring it in the .gitconfig file does work

Cause

TeamCity propagates the proxy settings via envvars, in particular the http_proxy, htts_proxy and no_proxy are configured based on teamcity's proxy settings. Git was ignoring them, or rather, only using the last domain on the no_proxy setting, due to a specific version of libcurl being the one taken by the server that wouldn't resolve the parameter correctly

Resolution

Check if libcurl v 4.5.0 is available. We have confirmed that version to work correctly. The issue in particular is not on TeamCity but on git itself, it just manifests on TeamCity due to the settings being configured through the envvars.

Workaround

Configuring the proxy exclusions in the .gitconfig file for agents should work, or changing the auth to SSH.