<firebase-auth> phone auth

[FluorescentHallucinogen]

Is it possible to use <firebase-auth> for phone number sign-in? Something like:

<firebase-auth user="{{user}}" provider="phone"></firebase-auth>

[tjmonsi]

As of now, no... But a PR would be lovely :) Will review how phone auth works based from docs

[FluorescentHallucinogen]

The phone auth is implemented in FirebaseUI for Web: https://github.com/firebase/firebaseui-web#configuring-sign-in-providers. Demo: https://fir-ui-demo-84a6c.firebaseapp.com.

@tjmonsi Could you please create a pull request?