Other useful information, I hope.
After uncommenting these three lines (as suggested here):
CapabilityBoundingSet=CAP_NET_BIND_SERVICE
AmbientCapabilities=CAP_NET_BIND_SERVICE
NoNewPrivileges=true
and a reboot, the unit starts successfully until I try to open localhost in my browser:
[~]$ systemctl status caddy
● caddy.service - Caddy HTTP/2 web server
Loaded: loaded (/etc/systemd/system/caddy.service; enabled; vendor preset: disabled)
Active: active (running) since lun 2017-04-17 21:09:33 CEST; 15min ago
Docs: https://caddyserver.com/docs
Main PID: 1101 (caddy)
Tasks: 7 (limit: 4915)
CGroup: /system.slice/caddy.service
└─1101 /usr/local/bin/caddy -log stdout -agree=true -conf=/etc/caddy/Caddyfile -root=/home/fede/public_html
apr 17 21:09:33 fedora systemd[1]: Started Caddy HTTP/2 web server.
apr 17 21:09:33 fedora caddy[1101]: Activating privacy features... done.
apr 17 21:09:33 fedora caddy[1101]: http://
apr 17 21:09:33 fedora caddy[1101]: 2017/04/17 21:09:33 http://
[~]$
[~]$ systemctl status caddy
● caddy.service - Caddy HTTP/2 web server
Loaded: loaded (/etc/systemd/system/caddy.service; enabled; vendor preset: disabled)
Active: failed (Result: start-limit-hit) since lun 2017-04-17 21:25:08 CEST; 10s ago
Docs: https://caddyserver.com/docs
Process: 3735 ExecStart=/usr/local/bin/caddy -log stdout -agree=true -conf=/etc/caddy/Caddyfile -root=/home/fede/public_html (code=exited, status=203/EXEC)
Main PID: 3735 (code=exited, status=203/EXEC)
apr 17 21:25:08 fedora systemd[1]: caddy.service: Unit entered failed state.
apr 17 21:25:08 fedora systemd[1]: caddy.service: Failed with result 'exit-code'.
apr 17 21:25:08 fedora systemd[1]: caddy.service: Service hold-off time over, scheduling restart.
apr 17 21:25:08 fedora systemd[1]: Stopped Caddy HTTP/2 web server.
apr 17 21:25:08 fedora systemd[1]: caddy.service: Start request repeated too quickly.
apr 17 21:25:08 fedora systemd[1]: Failed to start Caddy HTTP/2 web server.
apr 17 21:25:08 fedora systemd[1]: caddy.service: Unit entered failed state.
apr 17 21:25:08 fedora systemd[1]: caddy.service: Failed with result 'start-limit-hit'.