I'm the administrator & sysadmin for a Drupal site with a few thousand users. In maintaining the site, sometimes I need to troubleshoot issues reported by users that are difficult for me to reproduce when I'm logged in as me. Discrepancies in our abilities to reproduce the issue could be caused by (for example) roles and permissions or ownership of content. In any case, I'd like an easy way to log in as that particular user to test and troubleshoot the situation. And obviously I don't want to ask the the user tells me their password. Is there an easy way to do this?
Masquerade is what you need:
The Masquerade module allows site administrators (or anyone with enough permissions) to switch users and surf the site as that user (no password required). That person can switch back to their own user account at any time.