public class UserRepository : IUserRepository
    {
        private readonly SampleContext context;

        public UserRepository(SampleContext context)
        {
            this.context = context;
        }

        public async Task<User> GetUserAsync(string username, string password)
        {
            using (var userManager = new UserManager<IdentityUser>(new UserStore<IdentityUser>(context)))
            {
                var user = await userManager.FindByNameAsync(username);
                if (user == null)
                {
                    return null;
                }

                var correctPassword = await userManager.CheckPasswordAsync(user, password);
                if (correctPassword)
                {
                    return new User
                    {
                        UserName = username,
                        Email = user.Email,
                        Id = user.Id
                    };
                }
                return null;
            }
        }

        public async Task SignUpUserAsync(User user)
        {
            using (var userManager = new UserManager<IdentityUser>(new UserStore<IdentityUser>(context)
            {
                AutoSaveChanges = false
            }))
            {
                var result = await userManager.CreateAsync(new IdentityUser
                {
                    UserName = user.UserName,
                    Email = user.Email,
                    EmailConfirmed = true
                }, user.Password);

                if (!result.Succeeded)
                {
                    throw new InvalidOperationException("Sign up failed!");
                }
            }
        }
    }