title: How to sign JWT?
body: <p>I'm trying to secure a Sinatra API.</p>
  
  <p>I'm using <code>ruby-jwt</code> to create the JWT, but I don't know exactly what to sign it with.</p>
  
  <p>I'm trying to use the user's BCrypt <code>password_digest</code>, but every time <code>password_digest</code> is called it changes, making the signature invalid when I go to verify it.</p>