title: Authorization request (add to roster) using strophe.js
body: <p>I use <a href="https://github.com/metajack/strophejs">strophe.js</a> library to send and receive XMPP messages in browser. It works fine, but only for users I already have in my contact list - roster. </p>
  
  <p>I need to add someone (whose address I know) to my roster. How can I achieve this using strophe.js? This is important for me since gmail refuses sending messages to people I don't have in my roster. I'd like to get subscription: both, to be able to receive and send messages.</p>