title: .NET HttpClient. How to POST string value?
body: <p>How can I create using C# and HttpClient the following POST request:
  <img src="https://i.stack.imgur.com/yp8jr.png" alt="User-Agent: Fiddler Content-type: application/x-www-form-urlencoded Host: localhost:6740 Content-Length: 6"></p>
  
  <p>I need such a request for my WEB API service:</p>
  
  <pre><code>[ActionName("exist")]
  [HttpPost]
  public bool CheckIfUserExist([FromBody] string login)
  {           
      return _membershipProvider.CheckIfExist(login);
  }
  </code></pre>