// GET: api/Customer/username/password
        [HttpGet("{username}/{password}", Name = "Get")]
        public async Task<ActionResult<CustomerViewModel>> Login(string username, string password)
        {
            return Ok(await Mediator.Send(new LoginCustomerQuery { Username = username,Password = password }));
        }

public class LoginCustomerQuery : IRequest<CustomerViewModel>
    {
        public string Username { get; set; }
        public string Password { get; set; }
    }

public class CustomerViewModel
    {
        public Guid ExternalId { get; set; }
    }

public async Task<CustomerViewModel> Handle(LoginCustomerQuery request, CancellationToken cancellationToken)
        {
            var entity = await _context.Customers
                .Where(e =>
                e.Username == request.Username
                && e.Password == Encypt.EncryptString(request.Password))
                .FirstOrDefaultAsync(cancellationToken);

            if (entity.Equals(null))
            {
                throw new NotFoundException(nameof(entity), request.Username);
            }

            return new CustomerViewModel
            {
                ExternalId = entity.ExternalId
            };
        }