c# - Google API: How can I check if the authentication was done successfully? -

using google.apis.analytics.v3 library in .net, doing oauth2 authentication google analytics api, this:

string[] scopes = new string[] { analyticsservice.scope.analytics,  // view , manage analytics data                                              analyticsservice.scope.analyticsedit,  // edit management actives                                              analyticsservice.scope.analyticsmanageusers,   // manage users                                              analyticsservice.scope.analyticsreadonly};     // view analytics data  usercredential credential = googlewebauthorizationbroker.authorizeasync(                                 new clientsecrets { clientid = clientid, clientsecret = clientsecret }                                  , scopes                                  , username                                  , cancellationtoken.none                                  , new databasedatastore("analytics")).result;  analyticsservice service = new analyticsservice(new baseclientservice.initializer() {     httpclientinitializer = credential,     applicationname = "masterpiece" }); 

the problem @ end, don't know if authentication successful or not, don't see way of getting sort of message implementation. normally, works fine , can go on interrogating api. if revoke token have stored username, implementation not tell me service not authenticated , when try interrogate api afterwards error.

how in world should verify if authentication done before start accessing api methods? if authentication fails, want able remove revoke token data store, , try authentication again, asking user permission.

there few things can go wrong should consider.

1. the user click accept. no problem here can check credential.token.accesstoken see got access token , can access api.
2. the user not click accept clicks cancle instead. in instance exception throw. why code above should in try catch. [system.aggregateexception] innerexception = {"error:\"access_denied\", description:\"\", uri:\"\""}
3. third option user nothing in case code hang waiting result user. (bug report: still working on solution one)

now worry if delete user in databasedatastore happen. should happen same if there new user. if code in databasedatastore correct system detect doesn't have user , prompt user again authentication. client library should you, or rather databasedatastore should. recommend testing around user , filedatastore see how works. if yours not prompting new authentication when delete user system there wrong databasedatastore.

recommendations.

1. don't request scopes request need.
2. put code in try catch in event don't authentication going throw error need catch it.
3. test on accesstoken if worried it.