Absolutely. Assuming you have an installation of UrBackup working successfully with internet clients without SSL.
Install stunnel (https://www.stunnel.org/) on your UrBackup server. After the install, run the shortcut in the start menu to install it as a service. (Make sure it’s not running interactively before you try and start the service.)
Edit the stunnel configuration (run the “Edit stunnel.conf” shortcut in the start menu). Comment out every line in the file (by adding a ; to the beginning) except the following section, which you should edit as follows:
; TLS front-end to a web server
accept = 443
connect = 55414
cert = mycert.pem
; "TIMEOUTclose = 0" is a workaround for a design flaw in Microsoft SChannel
; Microsoft implementations do not use TLS close-notify alert and thus they
; are vulnerable to truncation attacks
TIMEOUTclose = 0
Basically, you are telling stunnel to redirect requests on port 443 (the standard https port) to port 55414 (the standard UrBackup http port). Save the config file.
Place your .pem certificate file in the same folder as the stunnel.conf file (C:\Program Files (x86)\stunnel\config\ on my system). Make sure the filename matches what you specified in the config file above.
Restart the stunnel service in Windows Services to load the config you just saved.
Now, if you navigate to https://localhost from the UrBackup server it should load the login page. You will get an SSL error because localhost doesn’t match the name on the certificate. That’s fine for now, we are just checking that stunnel is working.
At some point when you got your certificate your decided what domain name you were going to access your server as. Normally this is in the form of subdomain.doman.com, such as urbackup.example.com. Your SSL cert will be issued in that name and the url you use to access your server must match that name.
Make sure you setup your DNS properly for external requests. And make sure you open port 443 on your router (same way you did port 55415). And make sure you make an exception for stunnel in the Windows firewall for Domain (if present), Private, and Public (should be listed as an exception already, just need to check the other boxes).
If all that is set up correctly, from an internet client, you should be able to access https://urbackup.example.com and get the UrBakcup login page. You should not get an SSL error this time because your url matches the certificate. (Unless, of course, you are using a self-generated cert and then you will still get an error unless you have trusted the issuier of the cert, but that is another topic entirley.)
As the last step set the server URL in the UrBackup setting to https://urbackup.example.com (Settings / Server / Server URL)