Easier Firebase authentication with jQuery Deferred

firebase-auth-deferred.js

var db = new Firebase('https://demo.firebaseio.com')

var authenticate = (function(db) {
    var loggedIn,
        deferred = $.Deferred()

    var client = new FirebaseAuthClient(db, function(err, user) {
        loggedIn = !!user

        if (err) {
            deferred.reject(err)
        } else if (user) {
            deferred.resolve(user)
        }
    })

    return function(provider, options) {
        if (!loggedIn) client.login(provider, options)

        return deferred
    }
})(db)

authenticate('facebook').done(function(user) {
    console.log('Logged in as:', user)
}).fail(function(err) {
    console.log('Error:', err)
})

Nice! So in the angular world would the authenticate definition live in a factory and it'd be accessible from any controller where the factory was a dependency (like the call on line 24)? If so, would there also be a way to confirm they're logged in or would that require a separate factory?