title: Sending string via POST - unsupported media type or null parameter
body: <p>My controller cannot accept string via <code>POST</code> method. What could be wrong? When I create <code>HttpClient</code> and send content like this :</p>
  
  <pre><code>var content = new FormUrlEncodedContent(new []
  {
       new KeyValuePair&lt;string, string&gt;("signature", "someexamplecontent"), 
  });
  
  var response = await _client.PostAsync(path, content);
  </code></pre>
  
  <p>I'm getting an error: <code>415, Unsupported media type</code> and it not stepping into controller. Instead, when I use <code>PostAsJsonAsync</code> - stepping into but parameter <code>signature</code> is null.</p>
  
  <pre><code>var response = await _client.PostAsJsonAsync(path, content);
  </code></pre>
  
  <p>That's a method in a controller:</p>
  
  <pre><code>[HttpPost("generatecert")]
  public byte[] PostGenerateCertificate([FromBody] string signature)
  {      
  }
  </code></pre>