nix-config/packages/system/nebula-sign-cert/default.nix

{
  writeShellApplication,
  nebula,
  sops,
  coreutils,
  jq,
  ...
}:

writeShellApplication {
  name = "nebula-sign-cert";

  runtimeInputs = [
    nebula
    sops
    coreutils
    jq
  ];

  text = ''
    # ---------------------------------------------------------------------------
    # nebula-sign-cert
    #
    # Signs a new Nebula host certificate using the CA stored in a SOPS secrets
    # file and writes the resulting cert+key back into a (possibly different)
    # SOPS secrets file.
    #
    # The CA is read from:
    #   <ca-sops-file>  at YAML path  <ca-prefix>/ca-cert  and  <ca-prefix>/ca-key
    #
    # The new cert+key are written to:
    #   <host-sops-file>  at YAML paths
    #     <host-prefix>/<host-secret-name>-cert
    #     <host-prefix>/<host-secret-name>-key
    #
    # Usage:
    #   nebula-sign-cert \
    #     --name         <node-name>           # e.g. "nas" — used in the cert
    #     --ip           <overlay-ip/mask>     # e.g. "10.1.1.2/24"
    #     --ca-file      <path/to/ca-secrets.yaml>
    #     --ca-prefix    <sops-key-prefix>     # e.g. "pi5/nebula"
    #     --host-file    <path/to/host-secrets.yaml>
    #     --host-prefix  <sops-key-prefix>     # e.g. "jallen-nas/nebula"
    #     --host-secret-name <name>            # e.g. "nas" (cert stored as nas-cert/nas-key)
    #     [--groups  <group1,group2>]          # optional Nebula groups
    #     [--duration <duration>]              # e.g. "8760h0m0s" (1 year), default: CA lifetime
    #
    # All temp files are written to a private tmpdir and shredded on exit.
    # ---------------------------------------------------------------------------

    set -euo pipefail

    # ── argument parsing ────────────────────────────────────────────────────────
    NAME=""
    IP=""
    CA_FILE=""
    CA_PREFIX=""
    HOST_FILE=""
    HOST_PREFIX=""
    HOST_SECRET_NAME=""
    NEBULA_GROUPS=""
    DURATION=""

    usage() {
      echo "Usage: nebula-sign-cert \\"
      echo "         --name          <node-name> \\"
      echo "         --ip            <overlay-ip/mask> \\"
      echo "         --ca-file       <path/to/ca-sops-file.yaml> \\"
      echo "         --ca-prefix     <sops-key-prefix>  (e.g. pi5/nebula) \\"
      echo "         --host-file     <path/to/host-sops-file.yaml> \\"
      echo "         --host-prefix   <sops-key-prefix>  (e.g. jallen-nas/nebula) \\"
      echo "         --host-secret-name <name>          (e.g. nas) \\"
      echo "         [--groups       <group1,group2>] \\"
      echo "         [--duration     <8760h0m0s>]"
      exit 1
    }

    while [[ $# -gt 0 ]]; do
      case "$1" in
        --name)           NAME="$2";            shift 2 ;;
        --ip)             IP="$2";              shift 2 ;;
        --ca-file)        CA_FILE="$2";         shift 2 ;;
        --ca-prefix)      CA_PREFIX="$2";       shift 2 ;;
        --host-file)      HOST_FILE="$2";       shift 2 ;;
        --host-prefix)    HOST_PREFIX="$2";     shift 2 ;;
        --host-secret-name) HOST_SECRET_NAME="$2"; shift 2 ;;
        --groups)         NEBULA_GROUPS="$2";    shift 2 ;;
        --duration)       DURATION="$2";        shift 2 ;;
        -h|--help)        usage ;;
        *) echo "Unknown argument: $1"; usage ;;
      esac
    done

    # ── validate required args ──────────────────────────────────────────────────
    missing=()
    [[ -z "$NAME"             ]] && missing+=(--name)
    [[ -z "$IP"               ]] && missing+=(--ip)
    [[ -z "$CA_FILE"          ]] && missing+=(--ca-file)
    [[ -z "$CA_PREFIX"        ]] && missing+=(--ca-prefix)
    [[ -z "$HOST_FILE"        ]] && missing+=(--host-file)
    [[ -z "$HOST_PREFIX"      ]] && missing+=(--host-prefix)
    [[ -z "$HOST_SECRET_NAME" ]] && missing+=(--host-secret-name)
    if [[ ''${#missing[@]} -gt 0 ]]; then
      echo "error: missing required arguments: ''${missing[*]}"
      usage
    fi

    [[ -f "$CA_FILE"   ]] || { echo "error: CA secrets file not found: $CA_FILE";   exit 1; }
    [[ -f "$HOST_FILE" ]] || { echo "error: host secrets file not found: $HOST_FILE"; exit 1; }

    # Convert "a/b/c" prefix → sops extract path ["a"]["b"]["c"]
    prefix_to_sops_path() {
      local prefix="$1"
      local IFS='/'
      local result=""
      for segment in $prefix; do
        result+="[\"$segment\"]"
      done
      echo "$result"
    }

    CA_SOPS_PATH=$(prefix_to_sops_path "$CA_PREFIX")
    HOST_SOPS_PATH=$(prefix_to_sops_path "$HOST_PREFIX")

    # ── setup temp directory (cleaned up on exit) ───────────────────────────────
    TMPDIR=$(mktemp -d)
    cleanup() {
      # Shred all temp files before removing the directory
      find "$TMPDIR" -type f -exec shred -u {} \;
      rm -rf "$TMPDIR"
    }
    trap cleanup EXIT

    CA_CRT="$TMPDIR/ca.crt"
    CA_KEY="$TMPDIR/ca.key"
    HOST_CRT="$TMPDIR/host.crt"
    HOST_KEY="$TMPDIR/host.key"

    # ── extract CA cert and key from SOPS ──────────────────────────────────────
    echo "» Extracting CA from $CA_FILE ($CA_PREFIX)..."
    sops decrypt --extract "''${CA_SOPS_PATH}[\"ca-cert\"]" "$CA_FILE" > "$CA_CRT"
    sops decrypt --extract "''${CA_SOPS_PATH}[\"ca-key\"]"  "$CA_FILE" > "$CA_KEY"

    # ── build nebula-cert sign args ─────────────────────────────────────────────
    SIGN_ARGS=(
      sign
      -name     "$NAME"
      -ip       "$IP"
      -ca-crt   "$CA_CRT"
      -ca-key   "$CA_KEY"
      -out-crt  "$HOST_CRT"
      -out-key  "$HOST_KEY"
    )
    [[ -n "$NEBULA_GROUPS" ]] && SIGN_ARGS+=(-groups "$NEBULA_GROUPS")
    [[ -n "$DURATION" ]] && SIGN_ARGS+=(-duration "$DURATION")

    # ── sign the certificate ────────────────────────────────────────────────────
    echo "» Signing certificate for $NAME ($IP)..."
    nebula-cert "''${SIGN_ARGS[@]}"

    echo "» Certificate details:"
    nebula-cert print -path "$HOST_CRT"

    # ── write cert and key back into the host SOPS file ────────────────────────
    # sops set requires a JSON-encoded string value; use jq -Rs . to encode the
    # file contents and pipe via --value-stdin to avoid leaking secrets in ps.
    echo "» Writing ''${HOST_SECRET_NAME}-cert into $HOST_FILE ($HOST_PREFIX)..."
    jq -Rs . "$HOST_CRT" | sops set --value-stdin \
      "$HOST_FILE" \
      "''${HOST_SOPS_PATH}[\"''${HOST_SECRET_NAME}-cert\"]"

    echo "» Writing ''${HOST_SECRET_NAME}-key into $HOST_FILE ($HOST_PREFIX)..."
    jq -Rs . "$HOST_KEY" | sops set --value-stdin \
      "$HOST_FILE" \
      "''${HOST_SOPS_PATH}[\"''${HOST_SECRET_NAME}-key\"]"

    echo ""
    echo "✓ Done. Certificate for '$NAME' written to $HOST_FILE"
    echo "  Rebuild the host to apply: sudo nixos-rebuild switch --flake .#<hostname>"
  '';

  meta = {
    description = "Sign a Nebula host certificate using a CA stored in SOPS";
    mainProgram = "nebula-sign-cert";
  };
}