IM_NEW/User.WebApi/Controllers/Auth/LoginRequest.cs

using FluentValidation;

namespace IdentityService.WebApi.Controllers.Auth
{
    public class LoginRequest
    {
        public string UserName { get; set; }
        public string Password { get; set; }
    }

    public class LoginRequestValidator : AbstractValidator<LoginRequest>
    {
        public LoginRequestValidator()
        {
            RuleFor(x => x.UserName)
                .NotEmpty()
                .NotNull()
                .MaximumLength(20)
                .MinimumLength(5);

            RuleFor(x => x.Password)
                .NotEmpty()
                .NotNull()
                .MaximumLength(50)
                ;
        }
    }
}