Friends system?

Hi,

I work sometimes on my game project (GitHub - Richi2293/fpsgame: Open source fps game developed with Unreal Engine in free time) and I would like to understand how I could add a type of friend system.

I try to explain myself better, I mean that a user has the possibility to add a friend online and create a “party” and then play together (join together in the matchmaking).
This without the use of Steam, I opted to use a dedicated server.

Thanks