A good starting point IMO is the example in the :ssh user guide.

That shows the general shape of things (connect/session_channel/exec) but doesn’t really use the messages, or answer your original question.

For the “using the messages” part, take a look at how SSHEx does it - the whole file is worth reading, but this is where the actual {:ssh_cm, ...} messages get handled:

https://github.com/rubencaro/sshex/blob/9758aeba36d94efbac061a03e57d673fc031591f/lib/sshex.ex#L226-L250

For the second half, there are two behaviours that :ssh depends on but the one we care about is :ssh_client_key_api. That’s implemented by two modules supplied with :ssh, :ssh_file and :ssh_agent which use either files or the SSH agent. :ssh_file is the default, but you can pass an alternative implementation via the :key_cb option to :ssh.connect.

HOWEVER

:ssh_client_key_api has more moving parts than just “here is a key”, it also deals with known hosts. SSHEx includes an implementation you could use / model after:

https://github.com/rubencaro/sshex/blob/master/lib/sshex/configurable_client_keys.ex#L10-L26

If you are using OTP, it’s always worth checking out the official documentation. Here is how to configure custom keypairs for servers and the next paragraph is for clients: ssh — OTP 29.0.2 (ssh 6.0.1)

The parameters that can be sent to the client/daemon are also clearly documented, take a look through them: ssh — OTP 29.0.2 (ssh 6.0.1)

Ok I believe this is so easy for you so please just add that one line or 2 missing lines where I have put a placeholder for completion (my private key is located in /home/me/.ssh/id_ed25519)

ssh_options = [
      {:user, user},
      {:silently_accept_hosts, true},
      {:user_interaction, false},
      # ====== please just fill in here those easy missing lines ======
    ]

{:ok, conn} <- :ssh.connect(ip, port, ssh_options, 5000)

BTW I am really newbie to OTP, but I am sure you an experienced on these stuff.