Install FreeRADIUS:
apt-get install freeradius freeradius-mysql freeradius-utils
Allow all NAS clients to connect to it:
nano /etc/freeradius/3.0/clients.conf
Add the following lines at the end:
client all {
ipaddr = 0.0.0.0/0
secret = testing123
}
Authenticate all users without checking username/password:
nano /etc/freeradius/3.0/users
Add the following on top:
DEFAULT Auth-Type := Accept
Restart FreeRADIUS service:
systemctl restart freeradius.service