HttpListener::UnsafeConnectionNtlmAuthentication Property


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Gets or sets a Boolean value that controls whether, when NTLM is used, additional requests using the same Transmission Control Protocol (TCP) connection are required to authenticate.

Namespace:   System.Net
Assembly:  System (in System.dll)

property bool UnsafeConnectionNtlmAuthentication {
	bool get();
	void set(bool value);

Property Value

Type: System::Boolean

true if the IIdentity of the first request will be used for subsequent requests on the same connection; otherwise, false. The default value is false.

Exception Condition

This object has been closed.

When this property is set to true and the first request over a particular TCP connection is authenticated using NTLM, subsequent requests over the same TCP connection are processed using the authentication information (IIdentity) of the initial request.

This property has no effect when NTLM is not the authentication protocol. When Negotiate is specified as the authentication protocol, this property has an effect only if NTLM is the actual protocol used for authentication.


While setting this property to true increases performance because the HttpListener does not send additional NTLM authentication challenges, there is a security risk in not requiring all requests to provide authentication information. You must determine whether the increase in performance is worth this risk.

The following code example demonstrates setting this property.

public static void SimpleListenerWithUnsafeAuthentication(string[] prefixes)
    // URI prefixes are required,
    // for example "".
    if (prefixes == null || prefixes.Length == 0)
      throw new ArgumentException("prefixes");
    // Set up a listener.
    HttpListener listener = new HttpListener();
    foreach (string s in prefixes)
    // Specify Negotiate as the authentication scheme.
    listener.AuthenticationSchemes = AuthenticationSchemes.Negotiate;
    // If NTLM is used, we will allow multiple requests on the same
    // connection to use the authentication information of first request.
    // This improves performance but does reduce the security of your 
    // application. 
    listener.UnsafeConnectionNtlmAuthentication = true;
    // This listener does not want to receive exceptions 
    // that occur when sending the response to the client.
    listener.IgnoreWriteExceptions = true;
    // ... process requests here.


.NET Framework
Available since 2.0
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