This issue tested on version 2.4 and the new one, 2.5, on Mac but I think is also affecting the other versions.

Here is the issue description:

Due to some security policy inside the company where I work, I have to connect SourceTree applications to a test BitBucket server that is behind an Apache server with proxypass configured. The Apache server has a virtual host configured that has a public signed SSL certificate and require also client certificates.

The git client is working without any issue after it is configured with command
git config --global httpCert "<cn>"
(also works with local after the repository is downloaded from BitBucket server).

It works as expected when I configure SourceTree account to use BitBucket server and I disable client certificate authentication on Apache server, but as soon as reactivate the client certificate authentication it fails with the message seen in the print screen attached.

Is the SourceTree application capable to send client certificate when it is required to ?