Merge pull request #4263 from aik-jahoda/jajahoda/default_cred

Add proxy credentials remark to HttpHandler.UseDefaultCredentials

Author: davidsh

xml/System.Net.Http/HttpClientHandler.xml

@@ -1087,7 +1087,8 @@ handler.ServerCertificateCustomValidationCallback = HttpClientHandler.DangerousA
 
 ## Remarks
  Set this property to `true` when requests made by the <xref:System.Net.Http.HttpClientHandler> 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 <xref:System.Net.Http.HttpClientHandler.Credentials%2A> property to the credentials of the client on whose behalf the request is made.
-
+ 
+ This property doesn't affect proxy credentials. When the default (system) proxy is being used, set credentials explicitly by using the <xref:System.Net.Http.HttpClientHandler.DefaultProxyCredentials> property. When the proxy is set by the <xref:System.Net.Http.HttpClientHandler.Proxy> property, set credentials for the proxy via its <xref:System.Net.IWebProxy.Credentials> property.
  ]]></format>
         </remarks>
       </Docs>