title: Is "User-Agent" header mandatory in https GET request as per RFC
body: <h2>I was trying to download a file from a server using mbedtls.
  used the following GET request</h2>
  <p>GET /xxxxxxxxxxxxxxx.xml HTTP/1.1</p>
  <p>Host: example_xxxxx.com</p>
  <h2>Connection: keep-alive</h2>
  <p>The server responded with status 403</p>
  <p>When I add a &quot;User-Agent&quot; header filed, it started working.</p>
  <p>Is User-Agent mandatory for HTTP GET requests as per RFC specification.</p>