I fought this one for a while today.
There’s lots of documentation out there for using Composer with private repos and I got everything to work except getting the autoloader wired up. What finally worked for me was setting "no-api": true in the repositories key.
{
    "repositories": [
        {
            "type": "vcs",
            "url": "[email protected]:vendi-advertising/super-awesome-code.git",
            "no-api": true
        }
    ],
    "require": {
        "vendi-advertising/super-awesome-code": "dev-master",
    },
}