Plugin for token-based user registration?

Is there a plugin that will make use of user roles or groups that would automatically assign a new user to a specific role or group based on including a “token” or code word or something entered during registration?

I’m helping a colleague set up a WP site to use with clients who need to see different content depending what program they’re in. My thought was to use a roles or groups plugin to setup and manage the content permissions, and then to assign users to the appropriate role/group. The challenge is that ideally we’d like to have the role/group assignment happen automatically when the client registers on the site.

I thought about using an LMS plugin, but they all seem to be geared towards sites that are open to the public for course registration and/or show all the courses available so that a user can register for the course of their choice… in our situation it needs to be more restrictive — client registers and only has access to the appropriate resources, and doesn’t even see the other programs.

Any ideas?

Thanks,
Scott