Gradle file for getting maven dependencies hosted on private github repo

gistfile1.txt

repositories {
    mavenCentral()
    maven {
        url = 'https://github.com/github-username/github-project/raw/master'
        credentials {
            username 'my-username'
            password 'my-password'
        }
    }
}

dependencies {
    compile 'com.example:library_project:0.0.1'
}

I want to use authentication through ssh key. Where can I find the documentation on this?