How to get back to app after google login - xamarin.ios

Question

I'm trying to implement google login in my app using xamarin.auth like below
var auth = new OAuth2Authenticator("284202576320-7kgdhaa5sgvkoe03jmmcv0p8lfdma306.apps.googleusercontent.com","cAZW7uegD-h2-
tNMMf5q1UGQ","https://www.googleapis.com/auth/userinfo.email",new
Uri("https://accounts.google.com/o/oauth2/auth"),new
Uri("http://dev.myfav.restaurant/Account/LoginComplete"),new
Uri("https://accounts.google.com/o/oauth2/token"),null,true)
{
AllowCancel = true,
};
but Completed event not firing and its going to web page after login :(
I'm getting below error
i need to get back user to my app how can i achieve this ???? Can anyone help me on this please.
Thanks in advance

Answer 1

Hey follow these two examples one is using web view and one is using google sign in sdk for google auth.
https://timothelariviere.com/2017/09/01/authenticate-users-through-google-with-xamarin-auth/
and
https://developer.xamarin.com/samples/xamarin-forms/WebServices/OAuthNativeFlow/
So according to this issue reported by Mounika.Kola .I think u should refer that authenticator.Completed -= OnAuthCompleted is there in ur code. For reference just see these codes which i used for google authorization in Xamarin Forms.
void OnLoginClicked(object sender, EventArgs e)
{
string clientId = null;
string redirectUri = null;
switch (Device.RuntimePlatform)
{
case Device.iOS:
clientId = Constants.iOSClientId;
redirectUri = Constants.iOSRedirectUrl;
break;
case Device.Android:
clientId = Constants.AndroidClientId;
redirectUri = Constants.AndroidRedirectUrl;
break;
}
var authenticator = new OAuth2Authenticator(
clientId,
null,
Constants.Scope,
new Uri(Constants.AuthorizeUrl),
new Uri(redirectUri),
new Uri(Constants.AccessTokenUrl),
null,
true);
authenticator.Completed += OnAuthCompleted;
authenticator.Error += OnAuthError;
AuthenticationState.Authenticator = authenticator;
var presenter = new Xamarin.Auth.Presenters.OAuthLoginPresenter();
presenter.Login(authenticator);
}
async void OnAuthCompleted(object sender, AuthenticatorCompletedEventArgs e)
{
var authenticator = sender as OAuth2Authenticator;
if (authenticator != null)
{
authenticator.Completed -= OnAuthCompleted;
authenticator.Error -= OnAuthError;
}
User user = null;
if (e.IsAuthenticated)
{
// If the user is authenticated, request their basic user data from Google
// UserInfoUrl = https://www.googleapis.com/oauth2/v2/userinfo
var request = new OAuth2Request("GET", new Uri(Constants.UserInfoUrl), null, e.Account);
var response = await request.GetResponseAsync();
if (response != null)
{
// Deserialize the data and store it in the account store
// The users email address will be used to identify data in SimpleDB
string userJson = await response.GetResponseTextAsync();
user = JsonConvert.DeserializeObject<User>(userJson);
}
if (account != null)
{
store.Delete(account, Constants.AppName);
}
await store.SaveAsync(account = e.Account, Constants.AppName);
await DisplayAlert("Email address", user.Email, "OK");
}
}
I hope it helps you.

Answer 2

In iOS once you have completed the authentication with Xamarin.Auth you just need to dismiss the viewController and you will be put back in your app.
You do this subscribing to the Completed event of the OAuth2Authenticator
auth.Completed += (sender, e) =>
{
DismissViewController(true, null);
};

Answer 3

If the "Native UI" is used (the last parameter in the constructor is set to true), which means that external/system browser is used for login not WebView. So, on Android instead of WebView [Chrome] CustomTabs is used and on iOS instead of UIWebView (or WKWebView) SFSafariViewController is used.
With native UI user is leaving your app and the only way to return to your app is app-linking (or deep-linking) and this requires completely different approach.
1st you cannot use http[s] scheme for redirect_url (OK on Android it is possible, but on iOS not). Use custom scheme for that.
See the sample[s] (Xamarin.Forms ComicBook):
https://github.com/moljac/Xamarin.Auth.Samples.NugetReferences
And the docs in the repo:
https://github.com/xamarin/Xamarin.Auth/tree/master/docs