MacOS – Automatically mount AFP for Time Machine (without saving a password in plaintext)

I have a Linux box running Netatalk that I use to store Time Machine backups. My machine running OS X sees this as an AFP service and Time Machine is happy with this arrangement. The only issue is that I need to manually connect to the Linux machine. I can do this by pressing buttons in Finder or I can do this form a shell with a command that looks like this:

mount -t afp afp://user:password@domain.tld/location /Volumes/mntpnt

This lets me automate connecting to the server but now I have a password saved in a plaintext shell script. What's a better way to automate this? My goal is to automatically allow Time Machine to access the Linux Machine if it can be reached.

To automate something like this with SSH I would authenticate with a passwordless key. Is there a way to do that with AFP?

I also have the password in my OS X keychain and I'm not prompted for a password if I go through Finder to connect to the Linux machine. Is there a sensible way to access to use this from a shell script?

I can provide more info about the Netatalk setup if that helps but it seems like the issue is on the client side.