Why Doesn't HttpClient Pass Credentials with UseDefaultCredentials=true, While WebClient Does?

Understanding Credential Handling in HttpClient

When an application, particularly one using impersonation, needs to interact with a Windows service through an ASP.NET MVC Web API, it's crucial to forward the user's credentials. However, setting UseDefaultCredentials = true within a standard HttpClient instance often fails to achieve this.

The HttpClient vs. WebClient Difference

Interestingly, WebClient, when configured similarly, correctly transmits credentials. This difference highlights a key behavioral distinction between the two classes.

The Solution: Configuring HttpClientHandler

To correctly propagate credentials using HttpClient, you must explicitly configure the underlying HttpClientHandler:

<code class="language-csharp">var myClient = new HttpClient(new HttpClientHandler() { UseDefaultCredentials = true });</code>

This approach ensures that HttpClient properly sends the user's credentials, allowing the service to authenticate the request correctly. This resolves the credential propagation issue encountered when using UseDefaultCredentials directly on the HttpClient object.

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