Introduce SSH functionality

[Therzok]

Added SshAgentCredentials for querying ssh-agent, SshUserKeyCredentials
for authenticating with a given ssh key-pair.

Introduced UsernameQueryCredentials which returns the supported credential
types.

Authentication exceptions are now translated from libgit2.

Supersedes #852

[Therzok]

Taking some important bits into discussion:

• libgit2 removed support for libssh2 embedding. What is the best way to make cmake look for libssh2 in a relative directory if it's not installed system-wide?

• I'll have to update nativebinaries scripts to be able to deploy these things once I find out the above. So we can ship libssh2 + libgit2 binaries in one package! =D

• We need some test on these things. Taken from previous PR:

  The ssh tests are a bit of a hassle to set up, but you can copy the code from libgit2's Travis script. I would recommend having at least one test run there to make sure basic functionality doesn't get broken.

• Once we have a combination of packages, we can test both without and with SSH support, by conditionally checking that things throw a InvalidOperationException (probably should be a NotSupportedException) on querying SSH credentials when native binaries don't have support for that.

[Therzok]

cc @nulltoken

[Therzok]

I'll rebase this as soon as possible. And I would like to have this reviewed though.

[dannyzhan]

Hi Guys, how's going with ssh support in libgit2sharp?
I really need this feature in my project.
Thanks!

[Therzok]

@nulltoken It's rebased atm. The only problem is getting the libssh2 native binaries alongside libgit2 ones.

[carlosmn]

That part is what https://github.com/carlosmn/libgit2sharp/tree/cmn/managed-ssh was trying to bridge by not needing libssh2, but it would require our own version of the ssh library currently.

[Therzok]

Going down the route of having that managed ssh implementation can cause some issues such as:

• We're still shipping a ssh library, so the whole thing is still shipping a dependency (one of your arguments).
• libssh2 could be compiled to target mobile apps and as a result, making libgit2sharp a PCL could be easier.

This could work for now, I'm not saying no. If a PCL for SSH appears, it's easy to migrate. Just stating the available options.

[carlosmn]

We wouldn't be the vendors for that library, it's a dependency the same way libssh2 is a dependency. The problems come when we're responsible for the updates, not when we use a library.

Unfortunately there doesn't seem to be an ssh library with active support, so the point may be moot as we'd have to maintain some version of it.

I don't get why having to compile an extra C library would be easier than using managed library for ssh if you wanna run it on a phone, IIRC you can't load native code on Windows Phone anyhow.

[Therzok]

@carlosmn it all depends on the type of the project. In example, SSH.NET is a simple .NET 4.0 library (as opposed to being a PCL - Portable Class Library), which could then be used as a common library between all the projects you have (WinPhone, Android, iOS, etc). That means, this specific library won't work in a mobile context.

I was working on making LibGit2Sharp a PCL itself, so I could afterwards use it in a mobile application context, and ssh support would come via libssh2.

[CumpsD]

What's the status on this? What exactly is blocking SSH support right now?

[carlosmn]

There is still no good way to have ssh support in the libgit2 library that comes with the nuget packages. We've spent a lot of time and energy trying to find a solution to us becoming vendors of a crypto library, but so far no solution has presented itself. This has left little time to worry about landing this.

[CumpsD]

Sadly enough, I went with NGit to get SSH working, would've loved to use the cleaner API of libgit2sharp

[EvAlex]

Any updates on this? Crucial feature. The whole library is of no use without it.

[carlosmn]

SSH support is in the bindings; the shipped libgit2 doesn't because we do not want to ship third-party crypto software in our packages.

If there are missing features from this PR, please open a new one adding that.

[Therzok]

@carlosmn We should at least surface the API using feature checks.

[carlosmn]

libgit2 knows whether it was built with ssh support so it'll error out on its own. I'm not a fan of the idea of the bindings doing feature checks themselves.

[EvAlex]

Should there at least be a paragraph with all this info in README.md? I assure you, this matter is not absolutely clear to everyone willing to use this library. It would assist people a lot, if there was some guidance on ssh git checkout.

For myself, I didn't manage to get through and found a workaround with NGit. But that one is so ugly and so very very slow, that I'm not happy at all. Too bad.

[carlosmn]

Without a description (and a reasonable way) of how to use your own library, I don't know how useful that'd be.

[ssougnez]

I'm confused... Is it supported or not ? I'm trying to clone a repository using SSH but I really can't find the way to do so. Some comments on the project tends to say it is supported, other say the opposite. Is it possible to have a clear statement on this please?

I really think that issue should be addressed ASAP... Who wants to use password in their code while a SSH key can be used? Without this feature, this awesome library is quite limited.

Thanks a lot for your work

[leobuskin]

@ssougnez you can use libgit2sharp fork with SSH support based on @Therzok work, available in NuGet under 'LibGit2Sharp-SSH' name.

[rebizu]

@leobuskin what version is it a fork of ?

[dannyzhan]

sadly, I have to use git command directly to support SSH.