title: Looking for cross-site membership solution/services for my PHP websites
body: <p>My problem set:  I develop websites for multiple clients (PHP-based, mostly WordPress).  Many of these sites need a login/membership solution for subscription services, etc.  Is there some sort of web-based solution, ideally with a RESTful interface, that I could hook into to handle this stuff, instead of implementing on a per-site basis?</p>
  
  <p>Features I seek:</p>
  
  <ul>
  <li>RESTful interface</li>
  <li>One master account could handle multiple sets of users from different domains/sites.</li>
  </ul>
  
  <p>NOTES:</p>
  
  <ul>
  <li>OpenID would be the closest example, but I want users to be able to set their credentials from within the given sites.</li>
  </ul>
  
  <p>If this doesn't exist, might you have recommendations on creating such a system hosted on AWS cloud, for example?</p>
  
  <p>Thanks-</p>