I'm looking for a solution that lets me create classes in which the way to have a user enroll in the course is by being provided a "coupon" [link]. I'm not sure if this is possible, or if someone may have extended the platform for something like this.

Seems like something like Enroll by "paid invitiation".

Scenario is this: 

​Purchase of "coupon" to specific course...

• Somewhere (Odoo or otherwise) Person A buys the "coupon" for a one-person enrollment in a specific course. 
• This gives them some kind of [coded link]. 
• They provide the link to Person B.   (Maybe they email it, for example).

​Then...

• Person B follows the link and can use it to enroll in the specific course. 
• Once enrolled, the [link] is expired and can't be used again.

Any thoughts on the idea would be helpful, thanks!