Firebase Auth
This plugin allows you to log in through Firebase Auth for iOS 8.0+ and Android 4.0+.
This plugin allows you to log in through Email, Facebook, Twitter, Anonymously and thought Phone Numbers( which is currently only supported by iOS at this moment(Android was just added today will look into support) ). On Google sign in, it is technically supported but due to web view limitation, it may be hard or impossible to implement at the current moment. A free Google sign-in plugin is planned which will be helpful in implementing Google sign in. This plugin will also up security on the other free firebase plugins offered.
Why does this plugin cost money? 
this plugin has 26 APIs at launch( with more planned), took awhile to support (month and a half), and will require more upkeep than most of my other plugins.