With the current version of the Git plugin, the code assumes to find SSH executable in a specific directory. By default this installation directory for Git on Windows is "C:\ProgramFiles\Git\bin\ssh.exe" (32-bit) or "C:\ProgramFiles (x86)\Git\bin\ssh.exe" (64-bit). I am referring to this method in the plugin's source code:

https://github.com/jenkinsci/git-client-plugin/blob/master/src/main/java/org/jenkinsci/plugins/gitclient/CliGitAPIImpl.java#L1084

If the Git client was installed into a custom directory, it's impossible to configure known SSH credentials. The plugin will show an error message. I understand that you want to ensure that the Git installation should be the official Git client. However in our environment we require that each Job must be able to specify specific versions of all tools so we must be able to support side by side installs of different versions Git.

Would it be possible to extend the plugin to either determine the GIT & SSH executables in the PATH or allow the plugin to point to a custom GIT & SSH executable?