stateless auth for nancy

auth.cs

public static class Authentication {
    public const string Secret = "123@123";

    public static void Setup(IPipelines pipelines, Db db) {
        var c = new StatelessAuthenticationConfiguration(ctx => {
            var username = ctx.Request.Headers[Constants.HeaderUsername].FirstOrDefault();
            var hash = ctx.Request.Headers[Constants.HeaderHash].FirstOrDefault();
            if (String.IsNullOrEmpty(username)) {
                return null;
            }
            if (String.IsNullOrEmpty(hash)) {
                return null;
            }
            if (hash != HashUsername(username)) {
                return null;
            }
            var user = db.Users.FirstOrDefault(u => u.Username == username);
            if (user == null) {
                return null;
            }
            return new UserIdentity {
                UserName = username,
                User = user.AsDTO()
            };
        });
        StatelessAuthentication.Enable(pipelines, c);
    }

    public static string HashUsername(string username) {
        return String.Concat(username, Secret).Md5Hash();
    }
}