What is the difference between “Google+ sign in” and “Federated Log-in” and “Google Users Service”?

Question

I want to add social sign-in feature to my Google App Engine based application and hence want to add Google's authentication mechanism along with FB log-in.

I am confused because Google has provided at least 3 different ways to do this.

1. Google+ sign-in (https://developers.google.com/+/web/signin/server-side-flow)
2. Users service provided on Google App Engine
3. Federated Authentication (https://developers.google.com/appengine/articles/openid)

I would like to know which method is the most recent and which method is used widely?

Thanks,

Chandrashekhar

Answer 1

#1 Google+ Sign In allows users to log in via OAuth 2.0, but requires users to have Google Plus enabled. Google+ Sign In also provides additional functionality to the Google+ APIs such as sharing and social integration. However, you could just use standard OAuth 2.0 for login, which removes the Google+ requirement.

#2 Users Service is a Google App Engine API. It allows any user with a Google Account to login. This is different to OAuth 2.0 - it uses Googles standard login pages and you can use it right out of the box without having to configure any OAuth scopes etc. You can get going with this very quickly.

#3 Federated Login integrates the Open ID standard with the Google App Engine Users API. This allows your users to log in with an Open ID (ie credentials they have registered with an 'Open ID provider'), and you to use the standard Users Service API. There are many Open ID providers out there, including Google.

Your question states that you want to add a "social sign-in feature" along with "FB log-in". So, that basically rules #1 & #2 out. Unfortunately, Facebook (and Twitter) are not Open ID providers, so that kind of rules #3 out too. For these, you will need to implement their own authentication mechanisms (Facebook Login and Sign in with Twitter). There is a great boilerplate repo on GitHub that has some code (in python) to help you get going.