Add support for authentication

I’m fairly new at React, so this could be the wrong design entirely, but:

It looks like a good way to handle authentication is to write:

componentWillMount() {
  firebaseRef.onAuth(auth => this.setState({auth: auth}));
},
componentWillUnmount() {
  firebaseRef.offAuth(...);
},

It would be nice if ReactFire would handle dropping the current authentication state into a component’s state, instead of needing this custom code.

[jwngr]

Firebase Auth support is coming in ReactFire 2.0.0. Check out https://github.com/firebase/reactfire/pull/123.

[jwngr]

That definitely does seem like a good way to handle Firebase Authentication state. I don’t think it’s worth putting in ReactFire proper though. It already is only two lines of code and I don’t think the addition of the other user management methods really adds much to the library. It makes sense in AngularFire since we promisify the API and handle the digest loop for you automatically. Those don’t seem like huge selling points in React (especially the digest loop one). So, I think for now we’ll keep ReactFire minimal and not include authentication.