If you didn’t notice Cisco IOS routers can serve as CA (Certificate Authority) servers as well. The example configurations are easy to find on the cisco.com but the only trick to know when enrolling Cisco VPN client with IOS CA is the syntax you put as url – the string should look:
Whwre is the IP address of the Cisco rotuer I attach below screenshot so you can see what I mean.
Some references as well .

URL to use when enrolling with Cisco CA

PKI client enrol with cisco CA