I'm running several apps on Google App Engine. I am using the UserService for Authentication to be able to send emails on behalf of the user etc. and OAuth2 for API authorization.
I am now trying to publish the apps on the Google Apps Marketplace, but I received an email telling me it is required to use OAuth2 for authentication.
As I am just using the supported Google stack I assume there is a way to meet the requirements for publishing my apps on the Google Apps Marketplace but right now I'm stuck.
This is similar to another question. The challenge is that the User service is using still using OpenID. You'll need to use a Client library to authenticate the user.
Currently we use Openid 2.0 for user authentication and Oauth for authorization of other services. Openid 2.0 is deprecated and Google will not provide authentication using Open Id. For time line refer this link https://developers.google.com/+/api/auth-migration#timetable
So they are suggesting to use OpenidConnect for authentication of user. OpenIdConnect is a layer written over Oauth 2.0 for authentication of user.
For references visit http://openid.net/connect/ and https://developers.google.com/accounts/docs/OAuth2Login?hl=ja#appsetup
来源：https://stackoverflow.com/questions/21915001/how-to-use-oauth2-openid-connect-with-userservice