htpasswd-api
Small REST API made with Flask (python) to generate htpasswd files. The files can be used with nginx or apache. Groups are currently not supported.
You can look into vagrant-control if you need an interface.
License
[Creative Commons Attribution 3.0 Unported] [2] [2]: https://raw.github.com/Pheromone/htpasswd-api/master/LICENSE.txt
Note
Keep in mind that this project is closer to ALPHA than to STABLE. DO NOT use on production system.