linux - Is there a way to log into a machine using SSH without password?

I know ssh is to create a secure shell connection to a machine, and we call ssh username@ip_address to login the machine.

Is there a way that I won't need to enter the password when connecting via SSH, or let's say SCP, or a run a command using SSH on a remote machine?

I know there are ssh-keys, which allow particular users to login without entering passwords.

Is there any other way to achieve so, which doesn't involve keys? Like some change in the ssh configuration?