Support login with email or username for same user in ASP.NET Core

Thank you to all contributors, but I think this question deserves a more precise answer.

The default templates of ASP.NET Core Identity will always create users with both the email and username containing the same value. Then, the default login handler (either in AccountController.Login or the OnPostAsync method of the Login view) will always consume the "email" field as being the username, and call PasswordSignInAsync. Though the code seems to imply it's supporting emails, this method really only accepts a username. To add to the whole confusion, the view is making validation that you entered a valid email, but what you enter will eventually be searched in the NormalizedUserName field!

Thus, if you want to allow emails as well, as stated by Mark and Razvan, you can use _userManager.FindByEmailAsync to get the actual username of the user trying to log in, then call PasswordSignInAsync with the username.

As stated by Barry Dorrans: "No you're right. The templates end up with username and email being the same during registration, but fail to keep them in sync. There's work scheduled for 2.2 to fix this ugly mess.".

An open issue here.

1. You must change AccountViewModel.cs

   public class LoginViewModel
       {
           [Required]
           [Display(Name = "Логин/Email")]
           //[EmailAddress]
           public string Email { get; set; }
   
           [Required]
           [DataType(DataType.Password)]
           [Display(Name = "Пароль")]
           public string Password { get; set; }
   
           [Display(Name = "Запомнить меня")]
           public bool RememberMe { get; set; }
       }
   

2. AccountController.cs

   
   public async Task Login(LoginViewModel model, string returnUrl)
       {
           if (!ModelState.IsValid)
           {
               return View(model);
           }
   
   
       ApplicationUser user;
       if (model.Email.Contains("@"))
           user = UserManager.FindByEmail(model.Email);            
       else
           user = UserManager.FindByName(model.Email);
   
       var result = await SignInManager.PasswordSignInAsync(user.UserName, model.Password, model.RememberMe, shouldLockout: false);
       switch (result)
       {
           case SignInStatus.Success:
               return RedirectToLocal(returnUrl);
           case SignInStatus.LockedOut:
               return View("Lockout");
           case SignInStatus.RequiresVerification:
               return RedirectToAction("SendCode", new { ReturnUrl = returnUrl, RememberMe = model.RememberMe });
           case SignInStatus.Failure:
           default:
               ModelState.AddModelError("", "Неудачная попытка входа.");
               return View(model);
       }
   }