First you have to setup a project with google:
https://code.google.com/apis/console/?pli=1
There you will get your client ID, here we’ll use:
1010265353588-to2pjmgge2oceivlsbdc17e8dgq64hfa.apps.googleusercontent.com
On your webpage you can have a link to:
https://accounts.google.com/o/oauth2/v2/auth ? response_type = token & client_id = 1010265353588-to2pjmgge2oceivlsbdc17e8dgq64hfa.apps.googleusercontent.com & nonce & redirect_uri