Startup.cs

private readonly IDictionary<string, User> _users = new Dictionary<string, User>
{
    {
        "George", new User {
            Id =  1,
            UserName = "George",
            FirstName = "George",
            LastName = "Dyrrachitis",
            Password = "1234",
            DateOfBirth = new DateTime(1989, 10, 26)
        }
    }
};