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How to: Create a Custom Binding Using the SecurityBindingElement

Windows Communication Foundation (WCF) includes several system-provided bindings that can be configured but do not provide full flexibility when configuring all the security options that WCF supports. This topic demonstrates how to create a custom binding directly from individual binding elements and highlights some of the security settings that can be specified when creating such a binding. For more information about creating custom bindings, see Extending Bindings in Windows Communication Foundation.

Creating a Custom Binding

In WCF all bindings are made up of binding elements. Each binding element derives from the BindingElement class. For the standard system-provided bindings, the binding elements are created and configured for you, although you can customize some of the property settings.

In contrast, to create a custom binding, binding elements are created and configured and a CustomBinding is created from the binding elements.

To do this, you add the individual binding elements to a collection represented by an instance of the BindingElementCollection class, and then set the Elements property of the CustomBinding equal to that object. You must add the binding elements in the following order: Transaction Flow, Reliable Session, Security, Composite Duplex, One-way, Stream Security, Message Encoding, and Transport. Note that not all the binding elements listed are required in every binding.

SecurityBindingElement

Three binding elements relate to message level security, all of which derive from the SecurityBindingElement class. The three are TransportSecurityBindingElement, SymmetricSecurityBindingElement, and AsymmetricSecurityBindingElement. The TransportSecurityBindingElement is used to provide Mixed mode security. The other two elements are used when the message layer provides security.

Additional classes are used when transport level security is provided:

Required Binding Elements

There are a large number of possible binding elements that can be combined into a binding. Not all of these combinations are valid. This section describes the required elements that must be present in a security binding.

Valid security bindings depend on many factors, including the following:

  • Security mode.

  • Transport protocol.

  • The message exchange pattern (MEP) specified in the contract.

The following table shows the valid binding element stack configurations for each combination of the preceding factors. Note that these are minimal requirements. You can add additional binding elements to the binding, such as message encoding binding elements, transaction binding elements, and other binding elements.

Security Mode Transport Contract Message Exchange Pattern

Datagram

Request Reply

Duplex

Transport

Https

OneWayBindingElement

HttpsTransportBindingElement

HttpsTransportBindingElement

TCP

OneWayBindingElement

SSL or Windows StreamSecurityBindingElement

SSL or Windows StreamSecurityBindingElement

SSL or Windows StreamSecurityBindingElement

TcpTransportBindingElement

TcpTransportBindingElement

TcpTransportBindingElement

Message

Http

SymmetricSecurityBindingElement

SymmetricSecurityBindingElement

SymmetricSecurityBindingElement (authentication mode = SecureConversation)

CompositeDuplexBindingElement

OneWayBindingElement

OneWayBindingElement

HttpTransportBindingElement

HttpTransportBindingElement

HttpTransportBindingElement

Tcp

SecurityBindingElement

SecurityBindingElement

SymmetricSecurityBindingElement (authentication mode = SecureConversation)

TcpTransportBindingElement

TcpTransportBindingElement

TcpTransportBindingElement

Mixed (transport with message credentials)

Https

TransportSecurityBindingElement

TransportSecurityBindingElement

OneWayBindingElement

HttpsTransportBindingElement

HttpsTransportBindingElement

TCP

TransportSecurityBindingElement

SymmetricSecurityBindingElement (authentication mode = SecureConversation)

SymmetricSecurityBindingElement (authentication mode = SecureConversation)

OneWayBindingElement

SSL or Windows StreamSecurityBindingElement

SSL or Windows StreamSecurityBindingElement

SSL or Windows StreamSecurityBindingElement

TcpTransportBindingElement

TcpTransportBindingElement

TcpTransportBindingElement

Note that there are many configurable settings on the SecurityBindingElements. For more information, see SecurityBindingElement Authentication Modes.

For more information, see Secure Conversations and Secure Sessions.

Procedures

To create a custom binding that uses a SymmetricSecurityBindingElement

  1. Create an instance of the BindingElementCollection class with the name outputBec.

  2. Call the static method M:System.ServiceModel.Channels.SecurityBindingElement.CreateSspiNegotiationBindingElement(true), which returns an instance of the SymmetricSecurityBindingElement class.

  3. Add the SymmetricSecurityBindingElement to the collection (outputBec) by calling the Add method of the Collection of BindingElement class.

  4. Create an instance of the TextMessageEncodingBindingElement class and add it to the collection (outputBec). This specifies the encoding used by the binding.

  5. Create a HttpTransportBindingElement and add it to the collection (outputBec). This specifies that the binding uses the HTTP transport.

  6. Create a new custom binding by creating an instance of the CustomBinding class and passing the collection outputBec to the constructor.

  7. The resulting custom binding shares many of the same characteristics as the standard WSHttpBinding. It specifies message-level security and Windows credentials but disables secure sessions, requires that the service credential be specified out-of-band, and does not encrypt signatures. The last can be controlled only by setting the MessageProtectionOrder property as shown in step 4. The other two can be controlled using settings on the standard binding.

Example

Description

The following example provides a complete function to create a custom binding that uses a SymmetricSecurityBindingElement.

Code

// Create an empty CustomBinding to populate
CustomBinding binding = new CustomBinding();
// Create a SymmetricSecurityBindingElement.
SymmetricSecurityBindingElement ssbe =
    SecurityBindingElement.CreateSspiNegotiationBindingElement(true);
// Add the SymmetricSecurityBindingElement to the BindingElementCollection.
binding.Elements.Add(ssbe);
binding.Elements.Add(new TextMessageEncodingBindingElement());
binding.Elements.Add(new HttpTransportBindingElement());
return new CustomBinding(binding);

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