Experience shows that if a site like this is on the public Internet and gets popular enough, it becomes a big target and has a high likelihood of disastrous compromise. Note well the responses in this extensive discussion (about a somewhat different goal):

• How should I ethically approach user password storage for later plaintext retrieval? - Stack Overflow

If you choose to go ahead, make sure you warn your users of the very real risks. Defense-in-depth is mandatory - keep the actual password storage machine off the web, accessed thru the firewall with a very simple interface, built on the most secure platform you can find, with lots of hardening and monitoring, a good IDS, etc etc.

Experience shows that if a site like this is on the public Internet and gets popular enough, it becomes a big target and has a high likelihood of disastrous compromise. Note well the responses in this extensive discussion (about a somewhat different goal):

• How should I ethically approach user password storage for later plaintext retrieval? - Stack Overflow

If you choose to go ahead, make sure you warn your users of the very real risks. Defense-in-depth is mandatory - keep the actual password storage machine off the web, accessed thru the firewall with a very simple interface, built on the most secure platform you can find, with lots of hardening and monitoring, a good IDS, etc etc.