If you install BOINC using the package manager (yum or apt), all users on your system will be able to control BOINC; in particular, they'll be able to attach to any project.

If you're the only user of your computer, that's OK. If there are other users, and you don't want them to control BOINC, do the following:

sudo rm /var/lib/boinc/gui_rpc_auth.cfg
sudo usermod -a -G boinc $USER
exec su $USER
sudo systemctl restart boinc-client

This will add you to the 'boinc' group, and will create a new access control file readable only by members of that group. If you want to let other users control BOINC, add them to the group also.