ASP.NET MVC: Custom Login form & Registration form

Step 1: Open IdentityConfig class, then you can configure validation password as below

// Configure the application user manager used in this application. UserManager is defined in ASP.NET Identity and is used by the application.
public class ApplicationUserManager : UserManager<ApplicationUser>
{
    public ApplicationUserManager(IUserStore<ApplicationUser> store)
        : base(store)
    {
        //PasswordHasher = new CustomPasswordHasher();
    }

    public static ApplicationUserManager Create(IdentityFactoryOptions<ApplicationUserManager> options, IOwinContext context)
    {
        var manager = new ApplicationUserManager(new UserStore<ApplicationUser>(context.Get<ApplicationDbContext>()));
        // Configure validation logic for usernames
        manager.UserValidator = new UserValidator<ApplicationUser>(manager)
        {
            AllowOnlyAlphanumericUserNames = false,
            RequireUniqueEmail = true
        };

        // Configure validation logic for passwords
        manager.PasswordValidator = new PasswordValidator
        {
            RequiredLength = 6,
            RequireNonLetterOrDigit = false,
            RequireDigit = false,
            RequireLowercase = false,
            RequireUppercase = false,
        };

        // Configure user lockout defaults
        manager.UserLockoutEnabledByDefault = true;
        manager.DefaultAccountLockoutTimeSpan = TimeSpan.FromMinutes(5);
        manager.MaxFailedAccessAttemptsBeforeLockout = 5;

        // Register two factor authentication providers. This application uses Phone and Emails as a step of receiving a code for verifying the user
        // You can write your own provider and plug it in here.
        manager.RegisterTwoFactorProvider("Phone Code", new PhoneNumberTokenProvider<ApplicationUser>
        {
            MessageFormat = "Your security code is {0}"
        });
        manager.RegisterTwoFactorProvider("Email Code", new EmailTokenProvider<ApplicationUser>
        {
            Subject = "Security Code",
            BodyFormat = "Your security code is {0}"
        });
        manager.EmailService = new EmailService();
        manager.SmsService = new SmsService();
        var dataProtectionProvider = options.DataProtectionProvider;
        if (dataProtectionProvider != null)
        {
            manager.UserTokenProvider =
                new DataProtectorTokenProvider<ApplicationUser>(dataProtectionProvider.Create("ASP.NET Identity"));
        }
        return manager;
    }
}

Open AccountViewModels class, then change LoginViewModel and RegisterViewModel allows you to create and login with a usename

public class LoginViewModel
{
    //[Required]
    [Display(Name = "Email")]
    [EmailAddress]
    public string Email { get; set; }
    [Display(Name = "User Name")]
    [Required]
    public string UserName { get; set; }
    [Required]
    [DataType(DataType.Password)]
    [Display(Name = "Password")]
    public string Password { get; set; }
    [Display(Name = "Remember me?")]
    public bool RememberMe { get; set; }
}

public class RegisterViewModel
{
    [Required]
    [EmailAddress]
    [Display(Name = "Email")]
    public string Email { get; set; }
    [Display(Name = "User Name")]
    public string UserName { get; set; }    
    [Required]
    [StringLength(100, ErrorMessage = "The {0} must be at least {2} characters long.", MinimumLength = 6)]
    [DataType(DataType.Password)]
    [Display(Name = "Password")]
    public string Password { get; set; }
    [DataType(DataType.Password)]
    [Display(Name = "Confirm password")]
    [Compare("Password", ErrorMessage = "The password and confirmation password do not match.")]
    public string ConfirmPassword { get; set; }
}

Open AccountController, then change Register and Login action as below

//
// POST: /Account/Register
[HttpPost]
[AllowAnonymous]
[ValidateAntiForgeryToken]
public async Task<ActionResult> Register(RegisterViewModel model)
{
    if (ModelState.IsValid)
    {
        var user = new ApplicationUser { UserName = model.UserName, Email = model.Email };
        var result = await UserManager.CreateAsync(user, model.Password);
        if (result.Succeeded)
        {
            await SignInManager.SignInAsync(user, isPersistent: false, rememberBrowser: false);
            // For more information on how to enable account confirmation and password reset please visit http://go.microsoft.com/fwlink/?LinkID=320771
            // Send an email with this link
            //string code = await UserManager.GenerateEmailConfirmationTokenAsync(user.Id);
            //var callbackUrl = Url.Action("ConfirmEmail", "Account", new { userId = user.Id, code = code }, protocol: Request.Url.Scheme);
            //await UserManager.SendEmailAsync(user.Id, "Confirm your account", "Please confirm your account by clicking <a href=\"" + callbackUrl + "\">here</a>");
            return RedirectToAction("Index", "Home");
        }
        AddErrors(result);
    }
    // If we got this far, something failed, redisplay form
    return View(model);
}

//
// POST: /Account/Login
[HttpPost]
[AllowAnonymous]
[ValidateAntiForgeryToken]
public async Task<ActionResult> Login(LoginViewModel model, string returnUrl)
{
    if (!ModelState.IsValid)
    {
        return View(model);
    }
    // This doesn't count login failures towards account lockout
    // To enable password failures to trigger account lockout, change to shouldLockout: true
    var result = await SignInManager.PasswordSignInAsync(model.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("", "Invalid login attempt.");
            return View(model);
    }
}

Open Register and Login view, then change Email to Username

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