title: How can I implement exclusive/invite-only user registration?
body: <p>I'm creating a site with user auth, and I plan to limit access using either invites or some other method.</p>
  
  <p>The site is built on Node, Express, and MongoDB.  I plan to use Passport JS, mainly because it's the only method I've learned (this is my first personal project).</p>
  
  <p>The only idea I have is a "secret code" on the registration page.  Thus only those I've told the code can register.  I have a feeling there are more elegant or secure ways to handle this, and would love any recommendations!</p>