Updated SSH access (markdown)

SSH-access.md

@@ -16,3 +16,44 @@ We will provide a module for the sshd config and service in the future to simpli
 It is recommended to source `~/.nix-profile/etc/profile.d/nix-on-droid-session-init.sh` from `~/.profile`.
 
 Furthermore the login shell is not recognized yet, so you may start your desired shell manually once logged via ssh.
+
+## nix-on-droid config
+
+You can also use this snippet to ease the manual setup process:
+
+```nix
+let
+  sshdTmpDirectory = "${config.user.home}/sshd-tmp";
+  sshdDirectory = "${config.user.home}/sshd";
+  pathToPubKey = "...";
+  port = 8022;
+in
+{
+  build.activation.sshd = ''
+    $DRY_RUN_CMD mkdir $VERBOSE_ARG --parents "${config.user.home}/.ssh"
+    $DRY_RUN_CMD cat ${pathToPubKey} > "${config.user.home}/.ssh/authorized_keys"
+
+    if [[ ! -d "${sshdDirectory}" ]]; then
+      $DRY_RUN_CMD rm $VERBOSE_ARG --recursive --force "${sshdTmpDirectory}"
+      $DRY_RUN_CMD mkdir $VERBOSE_ARG --parents "${sshdTmpDirectory}"
+
+      $VERBOSE_ECHO "Generating host keys..."
+      $DRY_RUN_CMD ${pkgs.openssh}/bin/ssh-keygen -t rsa -b 4096 -f "${sshdTmpDirectory}/ssh_host_rsa_key" -N ""
+
+      $VERBOSE_ECHO "Writing sshd_config..."
+      $DRY_RUN_CMD echo -e "HostKey ${sshdDirectory}/ssh_host_rsa_key\nPort ${toString port}\n" > "${sshdTmpDirectory}/sshd_config"
+
+      $DRY_RUN_CMD mv $VERBOSE_ARG "${sshdTmpDirectory}" "${sshdDirectory}"
+    fi
+  '';
+
+  environment.packages = [
+    (pkgs.writeScriptBin "sshd-start" ''
+      #!${pkgs.runtimeShell}
+
+      echo "Starting sshd in non-daemonized way on port ${toString port}"
+      ${pkgs.openssh}/bin/sshd -f "${sshdDirectory}/sshd_config" -D
+    '')
+  ];
+}
+```