nixos_config/nixos/modules/services/oci-authorized-keys.nix

{ config, lib, pkgs, ... }:
let
  cfg = config.alisceon.ociAuthorizedKeys;
  home = config.users.users.${cfg.user}.home;
  sshDir = "${home}/.ssh";
  authorizedKeysFile = "${sshDir}/authorized_keys";
  staticAuthorizedKeys = config.users.users.${cfg.user}.openssh.authorizedKeys.keys or [ ];
  staticAuthorizedKeysText =
    (lib.concatStringsSep "\n" staticAuthorizedKeys)
    + lib.optionalString (staticAuthorizedKeys != [ ]) "\n";
  staticAuthorizedKeysFile = pkgs.writeText "static-authorized-keys-${cfg.user}" staticAuthorizedKeysText;

  fetchOciAuthorizedKeys = pkgs.writeShellApplication {
    name = "fetch-oci-authorized-keys";
    runtimeInputs = [
      pkgs.coreutils
      pkgs.curl
      pkgs.gnugrep
    ];
    text = ''
      install -d -m 0700 -o ${lib.escapeShellArg cfg.user} -g ${lib.escapeShellArg cfg.group} ${lib.escapeShellArg sshDir}

      if [ ! -e ${lib.escapeShellArg authorizedKeysFile} ]; then
        install -m 0600 -o ${lib.escapeShellArg cfg.user} -g ${lib.escapeShellArg cfg.group} /dev/null ${lib.escapeShellArg authorizedKeysFile}
      fi

      chown ${lib.escapeShellArg "${cfg.user}:${cfg.group}"} ${lib.escapeShellArg authorizedKeysFile}
      chmod 0600 ${lib.escapeShellArg authorizedKeysFile}

      append_keys() {
        while IFS= read -r key; do
          [ -n "$key" ] || continue
          grep -qxF -- "$key" ${lib.escapeShellArg authorizedKeysFile} || printf '%s\n' "$key" >> ${lib.escapeShellArg authorizedKeysFile}
        done < "$1"
      }

      append_keys ${lib.escapeShellArg staticAuthorizedKeysFile}

      metadata_keys="$(mktemp)"
      trap 'rm -f "$metadata_keys"' EXIT

      curl --fail --silent --show-error --location \
        --connect-timeout 3 \
        --max-time 10 \
        --retry 3 \
        --retry-delay 2 \
        --header ${lib.escapeShellArg "Authorization: Bearer Oracle"} \
        --output "$metadata_keys" \
        ${lib.escapeShellArg cfg.metadataUrl} || {
          echo "Unable to fetch OCI authorized_keys for ${cfg.user}; leaving existing keys unchanged"
          exit 0
        }

      append_keys "$metadata_keys"

      chown ${lib.escapeShellArg "${cfg.user}:${cfg.group}"} ${lib.escapeShellArg authorizedKeysFile}
      chmod 0600 ${lib.escapeShellArg authorizedKeysFile}
    '';
  };
in
{
  options.alisceon.ociAuthorizedKeys = {
    enable = lib.mkEnableOption "fetching SSH authorized_keys from OCI metadata";

    user = lib.mkOption {
      type = lib.types.str;
      default = "alisceon";
      description = "User whose authorized_keys file should be populated.";
    };

    group = lib.mkOption {
      type = lib.types.str;
      default = "users";
      description = "Group owner for the user's SSH files.";
    };

    metadataUrl = lib.mkOption {
      type = lib.types.str;
      default = "http://169.254.169.254/opc/v2/instance/metadata/ssh_authorized_keys";
      description = "OCI metadata endpoint containing SSH authorized keys.";
    };
  };

  config = lib.mkIf cfg.enable {
    systemd.services.fetch-oci-authorized-keys = {
      description = "Fetch OCI metadata authorized_keys for ${cfg.user}";
      wantedBy = [
        "sshd.service"
        "multi-user.target"
      ];
      before = [ "sshd.service" ];
      after = [ "network-online.target" ];
      wants = [ "network-online.target" ];
      serviceConfig = {
        Type = "oneshot";
        RemainAfterExit = true;
        StandardError = "journal+console";
        StandardOutput = "journal+console";
        TimeoutStartSec = "30s";
      };
      script = lib.getExe fetchOciAuthorizedKeys;
    };

    systemd.services.fetch-ssh-keys.enable = false;
  };
}