/// <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);
}