Rsync Symbiosis backup credentials

[latentexistence1]

I want to have Symbiosis rsync backups to my home server. I know to put the path in /etc/symbiosis/dns.d/backup.name, but where do I specify login credentials? I believe rsync uses SSH so either a certificate or password is required but I have no idea where to put that.

(I've already set up DDNS, exposed SSH through the firewall and created a user to receive the backups.)

[latentexistence1]

OK, I tried creating a ssh key as root and copying that to my home server, that seems to work - at least it does for running the upload-backup with sudo.

For reference, here's what I did:
Created a "symbiosis" user on my linux box
Allowed SSH on port 22 through my router firewall to the linux box
Configured the router with a dynamic DNS service

On the symbiosis server, put "symbiosis@homeserver.dynamic.dns:/home/symbiosis/backup" in /etc/symbiosis/dns.d/backup.name

Then:
sudo su -
ssh-keygen
ssh-copy-id symbiosis@homeserver.dynamic.dns

Synchronise the backups with

sudo /etc/symbiosis/backup.d/post-backup.d/99-upload-backup