Set this property to true when requests made by this System.Net.WebProxy object should, if requested by the server, be authenticated using the credentials of the currently logged on user. For client applications, this is the desired behavior in most scenarios. For middle tier applications, such as ASP.NET applications, instead of using this property, you would typically set the WebProxy.Credentials property to the credentials of the client on whose behalf the request is made.

The following table shows the effect of setting the WebProxy.UseDefaultCredentials value, based on the value of the WebProxy.Credentials property.

If WebProxy.UseDefaultCredentials is false, you can change the WebProxy.Credentials property to any credentials. If WebProxy.UseDefaultCredentials is true, changing the WebProxy.Credentials property from CredentialCache.DefaultCredentials (the value that is set when the WebProxy.UseDefaultCredentials property is set to true) will throw an exception.