 <p>You can use the <code>Windows.Web.Http.HttpClient</code> instead of <code>System.Net.Http.HttpClient</code>, i.e.:</p> <pre><code>HttpClient _httpClient = new HttpClient(); bool result = _httpClient.DefaultRequestHeaders.TryAppendWithoutValidation("Accept", "vnd.servicehost.v1+json"); var response = await _httpClient.GetAsync(uri); </code></pre>