support plugin

I have created a subdomain on my website at
I want to set up a support system. Tickets, maybe video calls. I am not sure what is available. I really like to use a free plugin about this.
Can someone propose one?
Also, I want to ask something about exactly this. I want a logged-in user on my main site to be able to get into this support system without logging in procedure. Is this possible? Also, I would like a user, if he/she first visits support to be able to login with his/her main site credentials. Can this be done?