Best practice for integrating a forum like *Invision* to Member Areas with a SINGLE log-in for clients?

I'm creating a website for a client with a fitness course. They have hundreds of filmed workout classes and programming. We're planning on including those through youtube links within the Member Areas>Video Gallery. They'd also like the ability for clients to be able to log their scores (on a forum) and to have the ability to have group coaching classes (like clubs/fb groups) to do nutrition coaching.

As we know, people have short attention spans, we want to make creating accounts and log-ins simple. I believe we'd lose people if they have to log in to multiple areas on a daily basis (i.e. member areas AND the forum).

Is there a way to have a single log in between the two? The member area will be a paid subscription, and only paid subscribers will be able to access the forum and community pages. Thanks in advance!!