public override void ApplyClientCredential(string clientIdentifier, HttpRequestMessage request)
 {
     if (clientIdentifier != null)
     {
         if (this.credential != null)
         {
             ErrorUtilities.VerifyHost(
                 string.Equals(this.credential.UserName, clientIdentifier, StringComparison.Ordinal),
                 "Client identifiers \"{0}\" and \"{1}\" do not match",
                 this.credential.UserName,
                 clientIdentifier
                 );
         }
     }
     OAuthUtilities.ApplyHttpBasicAuth(request.Headers, clientIdentifier, this.clientSecret);
 }