medium-14e592bf-6540-4029-afb3-59817e50d326.cs

public async Task<IActionResult> OnGetCallbackAsync(
   string returnUrl = null, 
   string remoteError = null)
{
   returnUrl = returnUrl ?? Url.Content("~/");
   if (remoteError != null)
   {
      ErrorMessage = $"Error from external provider: {remoteError}";
      return RedirectToPage("./Login", new {ReturnUrl = returnUrl});
   }
   var info = await _signInManager.GetExternalLoginInfoAsync();
   if (info == null)
   {
      ErrorMessage = "Error loading external login information.";
      return RedirectToPage("./Login", 
                            new { ReturnUrl = returnUrl  });
   }
   var queryNameId = from claim in info.Principal.Claims
                     where claim.Type == ClaimTypes.NameIdentifier
                     select claim;
   var nameIdClaim = queryNameId.FirstOrDefault();
   await _signInManager.SignOutAsync();
   var user = new IdentityUser
   {
      UserName = nameIdClaim.Value,
      Email = null
   };
   var result = await _userManager.CreateAsync(user);
   if (result.Succeeded)
   {
      var newUser = await _userManager.FindByIdAsync(user.Id);
      var eClaims = new List<Claim>
      {
         new Claim(".displayName", user.Id),
         new Claim(".externalNamedIdentitier",nameIdClaim.Value),
         new Claim(".loginProvider",info.LoginProvider)
      };
      // normalized id.
      await _userManager.AddClaimsAsync(newUser, eClaims);
      await _signInManager.SignInAsync(user, isPersistent: false);
      await _userManager.DeleteAsync(user); 
      return LocalRedirect(returnUrl);
   }
   return RedirectToPage("./Login", new { ReturnUrl = returnUrl });
}