On this libgit2sharp issue thread it is mentioned that this project has no support for client certificates at this time.
I am interested in adding support for this, but am not sure what it needed to achieve it. By submitting this as an issue here I'm hoping to discuss the issue and avoid any potential duplicated effort.

Reproduction steps

Try to clone any project with some application that uses libgit2 to achieve it, from a server that asks for a client certificate. Some concrete examples of this are neon and npm.
I'm assuming at this point that the same behavior holds for e.g. a pull as well as any other functionality that require interaction with a remote.

Expected behavior

I'd like the clone, pull etc to succeed.

Actual behavior

At this moment the exact error varies a bit depending on the actual application but it comes down to the server not authenticating the client application due to a missing certificate.

Version of libgit2 (release number or SHA1)

Any, as I'm discussing new functionality.

Operating system(s) tested

Windows, OS X, Ubuntu Linux