title: Post request to include 'Content-Type' and JSON
body: <p>I'm to work with goo.gl for URL shortening. I need to make the following request: </p>
  
  <pre><code>POST https://www.googleapis.com/urlshortener/v1/url
  Content-Type: application/json
  {"longUrl": "http://www.google.com/"}
  </code></pre>
  
  <p>my html:-</p>
  
  <pre><code>&lt;form method="post" action="https://www.googleapis.com/urlshortener/v1/"&gt;
      &lt;button type="submit"&gt; submit &lt;/button&gt;
  &lt;/form&gt;
  </code></pre>
  
  <p>how do i add the 'content-type' and json here? </p>