To achieve this we use this excelent gem that just makes everything very easy.
Sometimes we like to do our own apps where only users in our domain have access, and we use this gem to make sure Janrain and Devise only authenticates our users.
Add the gem to your Gemfile or require it depending on what you are using.
Then, just set your email RegExp somewhere on your code:
RPXNow.email_regexp = /@crowdint.com$/
For rails, you can put it on an initializer. Since this is authentication code, I usually put it on initializers/devise.rb
Crowd Interactive is a Ruby and Rails consultancy firm powered by a team of enthusiast engineers who love programming. We turn your ideas into web applications, and we like challenging projects. We also have a lot of experience in retail, so it doesn't matter if your idea is about something you'd like to sell, we can surely help you.