/// <summary>
/// Add a signature to a Hash of parameters. The signature will be generated
/// from the app secret and the provided parameters, and should be used
/// whenever signed data needs to be sent to GoCardless (e.g. when creating
/// a new subscription). The signature will be added to the hash under the
/// key signature.
/// </summary>
/// <param name="params">the parameters to sign</param>
/// <returns>the parameters with the new signature key</returns>
private static Utils.HashParams SignParams(Utils.HashParams @params)
{
var signature = Utils.GetSignatureForParams(@params, GoCardless.AccountDetails.AppSecret);
@params.Add("signature", signature);
return @params;
}