How do integrate Disqus for logging into a forum?

New to programming, but I'm working on a PHP/Laravel forum website and the owner wants to integrate Disqus for comments (to save money) and also logging into their forum.

1. What are the potential downfalls of Integrating Disqus in this way?
2. Is this even possible with Disqus API?
3. How do you do this?
4. If it's not possible what are alternatives to save money on comments?

Thank you, and please help.