As you all know, the default Identity provider provided in ASP.NET MVC has very strict password rules by default, such as requiring lowercase character, uppercase character, non-alphanumeric character and a number.

To config the password rules you need open IdentityConfig.cs and then configure the password rules that you want.

// Configure validation logic for passwords
manager.PasswordValidator = new PasswordValidator
    RequiredLength = 3,
    RequireNonLetterOrDigit = false,
    RequireDigit = false,
    RequireLowercase = false,
    RequireUppercase = false

You can change login password length, digit, lowercase, upercase...