Support Google SSO

[paulschreiber]

Description

Allow users to log in with Google Sign-In (aka Single Sign On / SSO).

Benefits

• Allows for easier account creation
• Reduces support requests for lost passwords and account resets
• Delegates significant security work to Google, who's better at it than you.

Additional context

https://developers.google.com/identity/sign-in/web/sign-in https://developers.google.com/identity/sign-in/ios

[jamiewildehk]

Also sign in with apple (they are going to block your IOS app updates at some point if you don't)

[paulschreiber]

Filed #44 to cover Sign in with Apple.