Unable to use SSH keys with TACACS configured.

My company uses LDAP and Remote Role Groups for BIG-IP authentication, and more or less followed the following KB article to configure SSH key-based authentication for an automation account:

https://support.f5.com/csp/article/K13454

Do read the KB article for caveats about potentially losing the SSH public key during OS upgrades.

Create a user on the BIG-IP for the automation account, either in the Configuration Utility or using tmsh. If you will only be using SSH key authentication for this user, the user doesn't have to be defined in your remote authentication provider (at least not for LDAP). For example, you can use "ansibleops" per jaikumar's answer. Set the user's shell to "Advanced shell" in the Configuration Utility, or "bash" if using tmsh to create the account.

Create the /home/ansibleops/.ssh directory on the BIG-IP, and copy the SSH public key to the authorized_keys file in that directory.

You should then be able to authenticate with:

ssh -i /path/to/ssh_private_key ansibleops@bigip.mycompany.com

I just ran these steps on my lab box, and it wasn't necessary to add the "ansibleops" user to /config/bigip/auth/localuser on BIG-IP 12.1.3.x. I can't speak to whether that's changed in newer versions.