How do I have 2 users associated with a model

I have a model that I want 2 users to have an association with. So this model would have a proposer (user) and a challenger (a different user). I am getting a bit tied up in spaghetti around whether this is a has_and_belongs_to_many relationship or I also saw a pattern where you can state belongs_to :proposer, class 'User'

I am relatively new to rails so apolgies if a stupid question!