title: Using browser's certificate (private key) to sign some string in javascript
body: <p>My users have some certificates (private keys) installed in their web browser. These certificates are used by the browser to authenticate the user on certain third party websites.</p>
  
  <p>I would like to <strong>sign</strong> some string <strong>using one of the private keys</strong>, when the user uses/visits <strong>my website</strong>. Is there any JavaScript API or function, which would enable to do this?</p>