title: Whats a decent way to upgrade from SHA1 to SHA256?
body: <p>I have an existing database with about 1.6 million users in it. Currently the passwords are stored as salted SHA1, I'd like to upgrade them all to salted SHA256.</p>
  
  <p>The approach I've taken so far if to migrate each user as they login, essentially validate their password against the old hash and if it matches create a new stronger hash. This works fine, but it's a slow process.</p>
  
  <p>As far as I can see there is no easy way to shortcut this process. Is there a better way?</p>