Google+ API Key is for Google Login.

Follow below steps to create Google+ API Key,

1. Go to Google API Console Page, https://console.developers.google.com

2. Create or Select Project.

3. Enable Google+ API in Library page.

4. On the Credentials page, get an OAuth client ID.

5. Choose Web application in Create Client ID page.

6. Enter your site URL in Authorized JavaScript origins textbox.

7. Enter Authorized redirect URIs,

Makent Redirect URI : SITE_URL/googleAuthenticate