If anyone is still looking or in need for the Letsencrypt solution for
fortigate here is a working process ( was testing it for the past few
weeks ) A linux VM ( CentOS 7 or 8 ) for the certbot installation and
the scripts downloaded from here (
Broad. Integrated. Automated.
The Fortinet Security Fabric brings together the concepts of convergence and consolidation to provide comprehensive cybersecurity protection for all users, devices, and applications and across all network edges.