Authentication with Google to access the Data of User like Google Calendar

Basically there are two approaches to acceess data from Google . Both have their own benefits 

1st approach -> Public API access

Login with your Gmail id . Go to that link Google console . Create a project , and open that project . 

On left side there is link APIs and auths . 

Click on Credentials , there is option Public API access create your own key .

Let suppose you want to get the Distance betwwen two addresses , So for that purpose you can use Google Api .

Ex https://maps.googleapis.com/maps/api/distancematrix/json?origins=delhi&destinations=gurgaon&key=AIzaSyAJ46gsr3-1BcigzrfWib7o92yIXDRRSR4

So in this purpose you can use Public Key because that data is Publically Available , So whenever you use google API that is publically available then go towards Public API key.

2nd Approach -> OAuth

OAuth means authentication is required to access Google Data . Let suppose you want to Social Authentication (login using Gmail ) , So for this purpose Authentication is required , there are a lot of APIs that google Provide like to access the data of Google Calendar of user etc

Login with your Gmail id . Go to that link Google console . Create a project , and open that project . 

On left side there is link APIs and auths . Click on Credentials , there is option Create client ID create your own key .

So whatever you API need from Google enable that API from google Console.

NOTE -> If you are in testing environment and test on localhost then provide 

EX  JAVASCRIPT ORIGINS-> http://localhost:8080 (If hit go from gapi client site(javascript))

REDIRECT URIS -> http://localhost:8080/oauth/callback/googleplus 

**** Be specific in URIS and JAVASCRIPT ORIGINS otherwise it give error origin-mismatch .

And be specific of using http or https . And if you have your own Domain name then provide that.

Thanks