Connect android backend endpoints and client using oauth2

I have a problem where I intend to authorize Android app with @ApiMethod on endpoint. I read a lot of documentation but I didn't solve the problem.

The main error I see in the logs is GoogleAuthException: Unknown.

I created a project in the Google Developers Console with two clients - one for Android and one for audience / web_id.

My client code in android:

mCredential = GoogleAccountCredential.usingAudience(this,"server:client_id:"+Constants.WEB_CLIENT_ID);
chooseAccount();

      

        
        
        
      

    

In onActivityResult get the account name:

@Override
    protected void onActivityResult(int requestCode, int resultCode,
                                    Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        switch (requestCode) {
            case REQUEST_ACCOUNT_PICKER:
                if (data != null && data.getExtras() != null) {
                    String accountName =
                            data.getExtras().getString(
                                    AccountManager.KEY_ACCOUNT_NAME);
                    if (accountName != null) {
                        mCredential.setSelectedAccountName(accountName);
                    }
                }
                break;

        }

      

        
        
        
      

    

Then I create an AsyncTask for the endpoint method of the call and add the credentials:

        BpmApiRegister.Builder builder = new BpmApiRegister.Builder(AndroidHttp.newCompatibleTransport(),new JacksonFactory(),mCredential)
                .setRootUrl(Constants.CLOUD_URL)//https://project_id.appspot.com/_ah/api/
                .setApplicationName("BPM");
            User user = createUser();
            BpmApiRegister registerapi = builder.build();

        try {
            return registerapi.create(user).execute();//PROBLEM HERE
        } catch (Exception e) {
            e.printStackTrace(); 
        }

      

        
        
        
      

    

Endpoint code:

@Api(name = "bpmApiRegister",version = "v1",resource = "users", namespace = @ApiNamespace(
        ownerDomain = "backend.myapplication.example.com",
        ownerName = "backend.myapplication.example.com",
        packagePath = "" ))

public class UserRegisterEndpoint {

    private static final Logger logger = Logger.getLogger(UserRegisterEndpoint.class.getName());

    @ApiMethod(name = "create",path="users",httpMethod = ApiMethod.HttpMethod.POST,
            scopes = {BackendConstants.EMAIL_SCOPE},
            clientIds = {
                    BackendConstants.WEB_CLIENT_ID,
                    BackendConstants.ANDROID_CLIENT_ID,
                    Constant.API_EXPLORER_CLIENT_ID},
            audiences = {BackendConstants.ANDROID_AUDIENCE})

    public User create(User user, com.google.appengine.api.users.User userAuth) throws OAuthRequestException {

      

        
        
        
      

    

Error in execution endpoint method:

04-25 11:00:11.655  19784-19927/com.android.app W/System.err﹕ com.google.android.gms.auth.GoogleAuthException: Unknown
04-25 11:00:11.655  19784-19927/com.android.app  W/System.err﹕ at com.google.android.gms.auth.GoogleAuthUtil.getToken(Unknown Source)
04-25 11:00:11.655  19784-19927/com.android.app W/System.err﹕ at com.google.android.gms.auth.GoogleAuthUtil.getToken(Unknown Source)

      

        
        
        
      

    

To create android client_id I got a fingerprint and I put it in com.android.app package (my app package).

To create a web_id, I put two urls http: // localhost: 8080 and https://project_id.appspot.com ; and our corresponding redirect url add / oauth2callback