Please follow these steps to let people authorize on your site with their Google accounts.
1. Go to the Google Developers Console.
2. Create a new project:
3. Go to the Library > Google+ API > enable Google+ API.
4. Now go to OAuth consent screen and insert data about your site:
4.1 If you need to change the logo, then be prepared for the fact that it will have to be verified by Google.
5. After that, return to Credentials and generate an OAuth cliend ID:
6. You will be asked to indicate the following information:
Authorized redirect URIs are: https://sitename.com/users_connections/oauth_login/3/ and https://sitename.com/admin/social_networking/oauth_active/3/1/
7. Copy the OAuth client ID and client secret:
8. Insert client ID and client secret in your site’s control panel under System > Social networks > Google > Application (/admin/social_networking/application/3/):
9. Finally, click the No button to initiate the connection:|