title: String too large for FormUrlEncodedContent() in Windows Phone 8 Post upload
body: <p>My code:</p>
  
  <pre><code>string json = BuildJson(uploadItem);
  
  using (var client = new HttpClient())
  {
      var values = new List&lt;KeyValuePair&lt;string, string&gt;&gt;();
      values.Add(new KeyValuePair&lt;string, string&gt;("parameter", json));
  
      var content = new FormUrlEncodedContent(values);
      var response = await client.PostAsync(App.Current.LoginUrl, content);
  
      var responseString = await response.Content.ReadAsStringAsync();
  }
  </code></pre>
  
  <p>My json string includes an base64 encoded image so the <code>FormUrlEncodedContent</code> throws the exception : </p>
  
  <blockquote>
    <p>" Invalid URI: The Uri string is too long".  </p>
  </blockquote>
  
  <p>Important is that the server expects exact this format with "parameter" as post key and the json as the post value. How can I bypass this limitation of <code>FormUrlEncodedContent</code>?</p>