Google/Facebook OAuth2 in Rails Front-end app with rails-api as webservice

First, you need to implement the google login in front-end. Here is google documentation on implementing google sign-in in javascript. google will provide you with information on user's profile. After you got the information, you can send it to you service. On server side/Backend you can do whatever with this information. That's on you.

Additionally, this documentation might be helpful for your case.

You could use omniauth-google-oauth2 gem

Main idea is to implement this into Devise.

Good solution You could find this.

With this solution, it is no problem if You use frontend/backend.So, You should pay attention on next steps:

User Model:

devise :database_authenticatable, ... , :omniauthable

Devise.rb:

config.omniauth :google_oauth2, ENV['GP_key'], ENV['GP_secret'],    {                  name: 'google',                  scope: 'plus.login, userinfo.email, userinfo.profile,                          ...                          youtubepartner, youtubepartner-channel-audit',                  prompt: "select_account"    }

Next steps as in solutions..

In my project it is workable with frontend/backend too.So, if you find difficulties, I will be glad do advice for it solving...

Update: for Android versions of frontend.You should not do authentication/authorization frontend on Google.You should do it on backend side.You could use webtools or other suitable ways for walking around Devise and Google auth pages...