SSH Authentication in git2go

I'm working on learning Go as my first compiled language (coming from php/python). My first project was a small POST hook listener for Bitbucket, which fetches and then checks out a Git repository via os/exec. I'm now trying to replace the os/exec calls with git2go. I'm running into a snag with the authentication, though. I have the following code:

package main

import (
	git "github.com/libgit2/git2go"
	"log"
)

func main() {

	_, Cred := git.NewCredSshKey("git","~/.ssh/id_rsa.pub","~/.ssh/id_rsa","")
	log.Println(Cred.Type())
	gitH,err := git.OpenRepository(".")
	if (err != nil) {
		log.Fatalln(err)
	}
	remotes,err := gitH.ListRemotes()
	if (err != nil) {
		log.Fatalln(err)
	}
	log.Println(remotes)
	origin,err := gitH.LoadRemote("origin")
	if (err != nil) {
		log.Fatalln(err)
	}
	err = origin.Fetch(nil,"")
	if (err != nil) {
		log.Fatalln(err)
	}
}

When I run this I get authentication required but no callback set.

Looking at the docs, it looks like I need to add a call to origin.SetCallbacks() which expects a RemoteCallbacks struct. RemoteCallbacks has the function CredentialsCallback which returns an int and a Cred pointer. Since NewCredSshKey returns the same values, I tried adding the following:

var cb git.RemoteCallbacks
cb.CredentialsCallback = git.NewCredSshKey("git","~/.ssh/id_rsa.pub","~/.ssh/id_rsa","")
origin.SetCallbacks(cb)

which gives the errors multiple-value git.NewCredSshKey() in single-value context and
cannot use cb (type git.RemoteCallbacks) as type *git.RemoteCallbacks in function argument.

I think I'm completely misunderstanding how this works, and I haven't been able to find any examples using this library. Tips or pointers to some examples would be much appreciated.

A Couple of things:

CredentialsCallback needs to be set to a function that matches it's signature, not the output of such a function. However, the signature for NewCredSshKey isn't correct in the first place, only its return values match. The correct signature is:

func(url string, username_from_url string, allowed_types CredType) (int, *Cred)

The second error cannot use cb (type git.RemoteCallbacks) as type *git.RemoteCallbacks is because you need a pointer to a RemoteCallbacks.

Either declare and initialize it as a pointer:

cb := &git.RemoteCallbacks{}
// or alternatively 
// cb := new(git.RemoteCallbacks)

or take the address of when passing it as an argument:

origin.SetCallbacks(&cb)