silverlight 访问 WCF 出现安全性错误的解决办法

最近在工作中使用Silverlight访问WCF报如下错误：System.Security.SecurityException: 安全性错误。经过资料查询，必须要在服务器端添加策略。

由于我使用的服务宿主程序为应用程序，所以将策略以文件流的形式承载在内存中。

      来看策略服务代码：

 using System.IO;
    using System.Reflection;
    using System.ServiceModel;
    using System.ServiceModel.Description;
    using System.ServiceModel.Web;

    using Common.MessageGateway.Interfaces;

    public class PolicyHepler
    {
        private PolicyHepler()
        {

        }

        private static PolicyHepler _Instance;
        public static PolicyHepler Instance
        {
            get
            {
                if ( _Instance == null )
                {
                    _Instance = new PolicyHepler();
                }
                return _Instance;
            }
        }

        public void LunchPolicy( string serviceUrl )
        {
            ServiceHost _policyhost = new ServiceHost( typeof( Policy ),new Uri( serviceUrl ) );
            ServiceEndpoint endpoint = _policyhost.AddServiceEndpoint( typeof( ISilverlightService ),new WebHttpBinding(),string.Empty );
            endpoint.Behaviors.Add( new WebHttpBehavior() );
            _policyhost.open();
        }
    }

    /// <summary>
    /// 获取策略文件
    /// </summary>
    public class PolicyForHttp : ISilverlightService
    {
        public Stream GetClientAccesspolicy()
        {
            if ( WebOperationContext.Current != null )
            {
                WebOperationContext.Current.OutgoingResponse.Headers.Add( "Content-Type","text/xml;charset=utf-8" );
            }
            return Assembly.GetExecutingAssembly().GetManifestResourceStream( "AI3.Server.VSMServer.VSS.clientaccesspolicy.xml" );
        }
    }

    #region nested type: Policy
    /// <summary>
    ///获取策略文件流
    /// </summary>
    [ServiceBehavior( InstanceContextMode = InstanceContextMode.PerCall )]
    public sealed class Policy : ISilverlightService
    {
        #region ICrossDomain Members

        public Stream GetClientAccesspolicy()
        {
            if ( WebOperationContext.Current != null )
            {
                WebOperationContext.Current.OutgoingResponse.Headers.Add( "Content-Type","text/xml;charset=utf-8" );
            }
            const string xml = @"<?xml version=""1.0"" encoding=""utf-8""?>
                                        <access-policy>
                                          <cross-domain-access>
                                            <policy>
                                              <allow-from http-request-headers=""*"">
                                                <domain uri=""*""/>
                                              </allow-from>
                                              <grant-to>
                                                <resource path=""/""
                                                          include-subpaths=""true""/>
                                              </grant-to>
                                            </policy>
                                          </cross-domain-access>
                                        </access-policy>";
            var array = Encoding.Default.GetBytes( xml );
            return new MemoryStream( array );
        }

        #endregion
    }

    #endregion

注意事项：发布策略服务的时候，IP和端口号和业务服务必须一致。