Create discourse URL response

DiscourseController.cs

private static string CreateDiscourseRedirectUrl(InMemoryUser user, string originalEncodedsso)
{
    var urlParameters = Parsesso(originalEncodedsso);
    var nonce = urlParameters.Get("nonce");
    var returnUrl = urlParameters.Get("return_sso_url");
    ValidateKnownurl(returnUrl);

    var ssoDictionary = new Dictionary<string, string>
    {
        {"nonce", nonce},
        {"email", HttpUtility.UrlEncode(user.GetClaim("email"))},
        {"external_id", HttpUtility.UrlEncode(user.Subject)},
        {"username", HttpUtility.UrlEncode(user.Username)},
        {"name", HttpUtility.UrlEncode(user.GetClaim("name"))}
    };

    var returnsso = CreatessoQueryString(ssoDictionary);

    var returnssoEncoded = Convert.ToBase64String(Encoding.UTF8.GetBytes(returnsso));
    var returnSig = Hash(DISCOURSE_SECRET, returnssoEncoded);

    return $"{returnUrl}?sso={returnssoEncoded}&sig={returnSig}";
}

private static NameValueCollection Parsesso(string encodedsso)
{
    var queryString = Encoding.UTF8.GetString(Convert.FromBase64String(encodedsso));
    return HttpUtility.ParseQueryString(queryString);
}

private static string CreatessoQueryString(Dictionary<string, string> dictionary)
{
    return string.Join("&", dictionary.Select(x => $"{x.Key}={x.Value}"));
}

private static string Hash(string secret, string encodedPayload)
{
  var hasher = new HMACSHA256(Encoding.UTF8.GetBytes(secret));
  var hash = hasher.ComputeHash(Encoding.UTF8.GetBytes(encodedPayload));
  return BitConverter.ToString(hash).Replace("-", "").ToLowerInvariant();
}

private List<string> ValidRedirectUris = new List<string>
{
    "http://discourse-test.westeurope.cloudapp.azure.com/session/sso_login"
};

private void ValidateKnownurl(string returnUrl)
{
    if (!ValidRedirectUris.Any(u => u.Equals(returnUrl)))
        throw new ApplicationException("Bad redirect uri");
}