/// <summary>
        /// Initializes a new instance of the
        /// <see cref="Google.Apis.Authentication.OAuth2.DotNetOpenAuth.AssertionFlowClient"/> class.
        /// </summary>
        /// <param name='authorizationServer'>
        /// Authorization server description.
        /// </param>
        /// <param name='certificate'>
        /// Certificate to use to sign the assertion flow messages.
        /// </param>
        public AssertionFlowClient(AuthorizationServerDescription authorizationServer,
                                   X509Certificate2 certificate) : base(authorizationServer, null, null)
        {
            certificate.ThrowIfNull("certificate");
            certificate.PrivateKey.ThrowIfNull("certificate.PrivateKey");

            Header      = new GoogleAssertionFlowHeader();
            Certificate = certificate;

            // Workaround to correctly cast the private key as a RSACryptoServiceProvider type 24
            RSACryptoServiceProvider rsa = (RSACryptoServiceProvider)certificate.PrivateKey;

            byte[] privateKeyBlob = rsa.ExportCspBlob(true);

            Key = new RSACryptoServiceProvider();
            Key.ImportCspBlob(privateKeyBlob);
        }
        /// <summary>
        /// Initializes a new instance of the
        /// <see cref="Google.Apis.Authentication.OAuth2.DotNetOpenAuth.AssertionFlowClient"/> class.
        /// </summary>
        /// <param name='authorizationServer'>
        /// Authorization server description.
        /// </param>
        /// <param name='certificate'>
        /// Certificate to use to sign the assertion flow messages.
        /// </param>
        public AssertionFlowClient(AuthorizationServerDescription authorizationServer,
                                   X509Certificate2 certificate) : base(authorizationServer, null, null) {
            certificate.ThrowIfNull("certificate");
            certificate.PrivateKey.ThrowIfNull("certificate.PrivateKey");

            Header = new GoogleAssertionFlowHeader();
            Certificate = certificate;

            // Workaround to correctly cast the private key as a RSACryptoServiceProvider type 24
            RSACryptoServiceProvider rsa = (RSACryptoServiceProvider) certificate.PrivateKey;
            byte[] privateKeyBlob = rsa.ExportCspBlob(true);

            Key = new RSACryptoServiceProvider();
            Key.ImportCspBlob(privateKeyBlob);
        }