How do I get the real error message in HttpClient response.ReasonPhrase?
<h2>My Setting</h2>

<p>I have 2 WebApi projects with the following flow:</p>

<ol>
<li><strong>User</strong> makes request to <strong>API 1</strong></li>
<li><strong>API 1</strong> makes request to <strong>API 2</strong> on behalf of the user (using an <code>HttpClient</code>).</li>
</ol>

<hr>

<pre><code>using (var client = new HttpClient())
{
    client.SetBearerToken(token);

    string endpoint = PbbSettings.Identity.Users.Delete.Replace("{userId}", userId);

    // Attempt deletion of the user
    using (var response = await client.DeleteAsync(endpoint))
    {
        // Throw exception if not succeeded
        EnsureSuccess(response);
    }
}
</code></pre>

<h2>The Problem</h2>

<p>So the flow of control and information works fine.
The problem is that when <strong>API 2</strong> responds with an error, <code>response.ReasonPhrase</code> says "Bad Request" or "Internal Server Error", instead of the message I set in the exception.</p>

<p>Been spitting blood on this for a whole day now. Any insights?</p>

<h2>More Info (TLDR)</h2>

<p>For clarity, all my APIs have a global exception filter registered to handle errors:</p>

<pre><code>public class RepositoryExceptionsHandlerAttribute : ExceptionFilterAttribute
{
    public override void OnException(HttpActionExecutedContext context)
    {
        HandleException(context);

        base.OnException(context);
    }

    public override Task OnExceptionAsync(HttpActionExecutedContext context, CancellationToken cancellationToken)
    {
        HandleException(context);

        return base.OnExceptionAsync(context, cancellationToken);
    }

    /// &lt;summary&gt;
    /// Recognizes common repository exceptions and if necessary creates a response and updates the context.
    /// &lt;/summary&gt;
    /// &lt;param name="context"&gt;The context in which the exception was thrown.&lt;/param&gt;
    private void HandleException(HttpActionExecutedContext context)
    {
        var response = CreateResponse(context.Request, context.Exception);

        if (response != null)
            context.Response = response;
    }

    /// &lt;summary&gt;
    /// Recognizes common repository exceptions and creates a corresponding error response.
    /// &lt;/summary&gt;
    /// &lt;param name="request"&gt;The request to which the response should be created.&lt;/param&gt;
    /// &lt;param name="ex"&gt;The exception to handle.&lt;/param&gt;
    /// &lt;returns&gt;An error response containing the status code and exception data, or null if this is not a common exception.&lt;/returns&gt;
    private HttpResponseMessage CreateResponse(HttpRequestMessage request, Exception ex)
    {
        string message = ex.Message;

        if (ex is KeyNotFoundException)        return request.CreateErrorResponse(HttpStatusCode.NotFound, message);
        if (ex is ArgumentException)           return request.CreateErrorResponse(HttpStatusCode.BadRequest, message);
        if (ex is InvalidOperationException)   return request.CreateErrorResponse(HttpStatusCode.BadRequest, message);
        if (ex is UnauthorizedAccessException) return request.CreateErrorResponse(HttpStatusCode.Unauthorized, message);
#if !DEBUG
        // For security reasons, when an exception is not handled the system should return a general error, not exposing the real error information
        // In development time, the programmer will need the details of the error, so this general message is disabled.
        request.CreateErrorResponse(HttpStatusCode.InternalServerError, Errors.InternalServerError);
#endif

        return null;
    }
}
</code></pre>

<p>This works fine between the <strong>user</strong> and <strong>API 1</strong>.
But when <strong>API 1</strong> and <strong>API 2</strong> do their thing, the response creation ignores the message I put in and sets the status as the reason.</p>