MSDN Magazine - April 2008 - (Page 54)

Figure 7 Implementing CodeAccessSecurityHelper (Partial) public static class CodeAccessSecurityHelper { public static void DemandClientPermissions (this ClientBase proxy, string operationName) where T : class { DemandClientConnectionPermissions(proxy.Endpoint); DemandTransactionPermissions(proxy.Endpoint,operationName); DemandTracingPermissions(); DemandClientSecurityPermissions(proxy); DemandEnvironmentPermissions(proxy); DemandClientStorePermissions(proxy.Endpoint); } internal static void DemandClientConnectionPermissions( ServiceEndpoint endpoint) { PermissionSet connectionSet = new PermissionSet(PermissionState.None); if(endpoint.Binding is NetTcpBinding) { connectionSet.AddPermission(new SocketPermission( NetworkAccess.Connect,TransportType.Tcp, endpoint.Address.Uri.Host,endpoint.Address.Uri.Port)); connectionSet.AddPermission(new DnsPermission( PermissionState.Unrestricted)); } /* Checking other bindings */ if(transactionFlow) { if(Transaction.Current != null) { //If operationName is null then at least one operation //needs to allow flow to trigger demand foreach(OperationDescription operation in endpoint.Contract.Operations) { string name = operationName ?? operation.Name; if(name != operation.Name) { continue; } foreach(IOperationBehavior behavior in operation.Behaviors) { if(behavior is TransactionFlowAttribute) { TransactionFlowAttribute attribute = behavior as TransactionFlowAttribute; if(attribute.Transactions != TransactionFlowOption.NotAllowed) { flowOptionAllowed = true; break; } } } if(flowOptionAllowed) { break; } } if(flowOptionAllowed) { IPermission distributedTransactionPermission = new DistributedTransactionPermission( PermissionState.Unrestricted); distributedTransactionPermission.Demand(); } } } } /* Rest of the bindings */ } connectionSet.Demand(); internal static void DemandTransactionPermissions( ServiceEndpoint endpoint) { DemandTransactionPermissions(endpoint,null); } internal static void DemandTransactionPermissions( ServiceEndpoint endpoint, string operationName) { bool transactionFlow = false; bool flowOptionAllowed = false; if(endpoint.Binding is NetTcpBinding) { NetTcpBinding tcpBinding = endpoint.Binding as NetTcpBinding; transactionFlow = tcpBinding.TransactionFlow; } } //Rest of the implementation .NET Framework that were designed for use in a partial-trust environment in a similar context, and I relied on the same demands as those. Finally, in the other cases, to compensate for suppressing the full trust demands, I used experience, familiarity with CAS, and common sense to map WCF activities to demands for dedicated permission types. When the WS-Dual Unmanaged code access is binding is used, Invoke demands Web permission to a highly privileged security connect to the target endpermission, granted only to point, as with any other the most trustworthy code. HTTP binding. However, to allow for hosting the callback object it also demands minimal ASP.NET hosting permission and Web permission to accept the calls to the callback address. When the MSMQ binding is used, Invoke demands MSMQ permission to send messages to the target queue. With any attempt to propagate the client’s transaction to a service, 54 msdnmagazine Foundations Invoke demands unrestricted distributed transaction permission. In this case, a transaction-aware binding is used, the transaction flow is enabled in the binding, the transaction flow at the operation level is allowed, and the client has an ambient transaction. Any attempt by the proxy to access the certificate store triggers demands for permission to enumerate the certificate stores, to open a store, and to enumerate the certificates in a store. This will happen when the client uses certificate credentials, or when message security is used and the client needs to validate the negotiated service certificate, or when the client does not negotiate a certificate and instead just loads a certificate to use for securing the message. When the client uses WCF diagnostics, Invoke demands environment permission to read the computer name and file I/O permission for the log and trace files used. Implementing Client-Side Structured Demands As mentioned already, the demands are carried out by CodeAccessSecurityHelper, whose partial implementation is shown in

Table of Contents Feed for the Digital Edition of MSDN Magazine - April 2008

MSDN Magazine - April 2008 Contents Toolbox CLR Inside Out Basic Instincts Cutting Edge Foundations Test Run Service Station Windows with C++ Going Places { End Bracket }

MSDN Magazine - April 2008

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