I’m developing a sister website to a well-established private site that is already built in WordPress. I can’t use WordPress to create what I need and I am therefore using Drupal. The owners of the WordPress site do not want their users to have to go through a separate login process to get into the Drupal site and would like their users to be able to click a link to the Drupal site and automatically be logged into the Drupal site, based on their WordPress credentials.
I know this must be possible, but where should I start, what do I need to know/learn in order to do this?
