Invite friend from another web server

Hello,
@Tobias , @vadim

i have one web server from there i login and create a private room with max player 5 players. and i want to invite 5 friend from same server from which i login and active currently so if i get active friends list from server than how can i send invitation to all friends and if they accept than all request accepted player redirected to room which was created by me and play game with friends. i don't want facebook friends but i want friends who logged in with same server which i use..

so please give me some guidance how to work on this features.

Thank You,