Link: https://sites.google.com/site/oauthgoog/Home/emaildisplayscope
From the link above I add the email scope
https://www.googleapis.com/auth/plus.me
https://www.googleapis.com/auth/userinfo.email
But I dont understand the following
Once you have a valid OAuth token, you can use it to make API calls to the Email Display API endpoint: https://www.googleapis.com/userinfo/email If the token is not valid, a 401 error will be returned. If the token is valid, then the user's Email address will be returned. The API will also return a boolean value to indicate whether Google has verified that the user owns that Email address. However most installed applications will ignore that value.
How to make a call to the Email Display API endpoint? Using https://www.googleapis.com/userinfo/email