The long wait since the first feature request in 2015 is finally over: with the latest Beta 1 release dated 24 September 2018, Let's Encrypt is now officially integrated into the Sophos UTM Firewall.
For anyone wondering what Let's Encrypt is:
Let's Encrypt is an alternative to the major certificate providers, with the difference that it offers free certificates valid for three months. The catch with these certificates is:
They have to be renewed every three months (the Sophos UTM Firewall now takes care of this for us)
You cannot get EV certificates. For these, you will still need a paid certificate.
The next question is usually: where can I use this certificate?
WAF (Web Application Firewall)
User interface
Webadmin
Hotspot portal
Where should you definitely not use the certificate? For SSL VPN, as the certificate is part of the configuration and has to be renewed regularly.
Installation
Let's Encrypt in the UTM
As with almost everything in the UTM, you need to enable this feature before you can use it. To do this, open Certificate Management and go to Advanced, where you will find the option to enable Let's Encrypt.
With the groundwork in place, you now need to create a certificate under Certificates for each domain you want to use. Both standard and SAN certificates are supported.
The certificate can now be used throughout the UTM.