ExternalLoginCallback action in asp.net core

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In this video, we will discuss how to handle login information received from the external login provider such as Google for example. This is continuation to our previous video. Please watch Part 106 from ASP.NET core tutorial before proceeding.


We will be redirected to Google sign-in page, if we click on the Google button on the Login view.




The following is the ExternalLogin action in AccountController that redirects the user to the external login provider sign-in page, in this case Google. We discussed this in detail in our previous video.

[AllowAnonymous]
public IActionResult ExternalLogin(string provider, string returnUrl)
{
    var redirectUrl = Url.Action("ExternalLoginCallback", "Account",
        new { ReturnUrl = returnUrl });
    var properties = signInManager
        .ConfigureExternalAuthenticationProperties(provider, redirectUrl);
    return new ChallengeResult(provider, properties);
}

Upon successful authentication, Google redirects the user back to our application and the following ExternalLoginCallback action is executed.

[AllowAnonymous]

public async Task<IActionResult>

            ExternalLoginCallback(string returnUrl = null, string remoteError = null)

{

    returnUrl = returnUrl ?? Url.Content("~/");

    LoginViewModel loginViewModel = new LoginViewModel

    {

        ReturnUrl = returnUrl,

        ExternalLogins =

                (await signInManager.GetExternalAuthenticationSchemesAsync()).ToList()

    };

    if (remoteError != null)

    {

        ModelState

            .AddModelError(string.Empty, $"Error from external provider: {remoteError}");

        return View("Login", loginViewModel);

    }

    // Get the login information about the user from the external login provider

    var info = await signInManager.GetExternalLoginInfoAsync();

    if (info == null)

    {

        ModelState

            .AddModelError(string.Empty, "Error loading external login information.");

        return View("Login", loginViewModel);

    }

    // If the user already has a login (i.e if there is a record in AspNetUserLogins

    // table) then sign-in the user with this external login provider

    var signInResult = await signInManager.ExternalLoginSignInAsync(info.LoginProvider,

        info.ProviderKey, isPersistent: false, bypassTwoFactor: true);

    if (signInResult.Succeeded)

    {

        return LocalRedirect(returnUrl);

    }

    // If there is no record in AspNetUserLogins table, the user may not have

    // a local account

    else

    {

        // Get the email claim value

        var email = info.Principal.FindFirstValue(ClaimTypes.Email);

        if (email != null)

        {

            // Create a new user without password if we do not have a user already

            var user = await userManager.FindByEmailAsync(email);

            if (user == null)

            {

                user = new ApplicationUser

                {

                    UserName = info.Principal.FindFirstValue(ClaimTypes.Email),

                    Email = info.Principal.FindFirstValue(ClaimTypes.Email)

                };

                await userManager.CreateAsync(user);

            }

            // Add a login (i.e insert a row for the user in AspNetUserLogins table)

            await userManager.AddLoginAsync(user, info);

            await signInManager.SignInAsync(user, isPersistent: false);

            return LocalRedirect(returnUrl);

        }

        // If we cannot find the user email we cannot continue

        ViewBag.ErrorTitle = $"Email claim not received from: {info.LoginProvider}";

        ViewBag.ErrorMessage = "Please contact support on Pragim@PragimTech.com";

        return View("Error");

    }

}