feat: add NATS NKey authentication support

Allow authentication to NATS using NKey seed files as an alternative to
credentials files. NKeys use Ed25519 key pairs for authentication.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

README.md

@@ -48,6 +48,7 @@ nix build
 | `--flake.nats.url` | `nats://localhost:4222` | NATS server URL |
 | `--flake.nats.subject` | `nixos-exporter.remote-rev` | NATS subject for revision updates |
 | `--flake.nats.credentials-file` | | NATS credentials file (optional) |
+| `--flake.nats.nkey-seed-file` | | NATS NKey seed file (optional) |
 
 ## NixOS Module Options
 
@@ -68,6 +69,7 @@ services.prometheus.exporters.nixos = {
       url = "nats://localhost:4222";
       subject = "nixos-exporter.remote-rev";
       credentialsFile = null;  # Optional path to credentials file
+      nkeySeedFile = null;     # Optional path to NKey seed file
     };
   };
 };

collector/flake.go

@@ -33,6 +33,7 @@ type FlakeCollectorConfig struct {
 	NATSURL             string
 	NATSSubject         string
 	NATSCredentialsFile string
+	NATSNkeySeedFile    string
 }
 
 // nixosVersionInfo holds the parsed output of nixos-version --json
@@ -107,7 +108,7 @@ func NewFlakeCollectorWithNATS(cfg FlakeCollectorConfig) (*FlakeCollector, error
 		c.natsEnabled = true
 		c.natsSubject = cfg.NATSSubject
 
-		if err := c.connectNATS(cfg.NATSURL, cfg.NATSCredentialsFile); err != nil {
+		if err := c.connectNATS(cfg.NATSURL, cfg.NATSCredentialsFile, cfg.NATSNkeySeedFile); err != nil {
 			// Log warning but continue without NATS
 			slog.Warn("Failed to connect to NATS, continuing without cache sharing", "error", err)
 		}
@@ -333,7 +334,7 @@ func getNixosVersionInfo() (*nixosVersionInfo, error) {
 }
 
 // connectNATS establishes connection to NATS server with auto-reconnect
-func (c *FlakeCollector) connectNATS(url, credentialsFile string) error {
+func (c *FlakeCollector) connectNATS(url, credentialsFile, nkeySeedFile string) error {
 	opts := []nats.Option{
 		nats.MaxReconnects(-1), // Infinite reconnects
 		nats.ReconnectWait(5 * time.Second),
@@ -363,6 +364,12 @@ func (c *FlakeCollector) connectNATS(url, credentialsFile string) error {
 
 	if credentialsFile != "" {
 		opts = append(opts, nats.UserCredentials(credentialsFile))
+	} else if nkeySeedFile != "" {
+		opt, err := nats.NkeyOptionFromSeed(nkeySeedFile)
+		if err != nil {
+			return fmt.Errorf("failed to load NKey seed file: %w", err)
+		}
+		opts = append(opts, opt)
 	}
 
 	nc, err := nats.Connect(url, opts...)

config/config.go

@@ -17,6 +17,7 @@ type Config struct {
 	FlakeNATSURL             string
 	FlakeNATSSubject         string
 	FlakeNATSCredentialsFile string
+	FlakeNATSNkeySeedFile    string
 }
 
 func Parse() (*Config, error) {
@@ -32,6 +33,7 @@ func Parse() (*Config, error) {
 	flag.StringVar(&cfg.FlakeNATSURL, "flake.nats.url", "nats://localhost:4222", "NATS server URL")
 	flag.StringVar(&cfg.FlakeNATSSubject, "flake.nats.subject", "nixos-exporter.remote-rev", "NATS subject for revision updates")
 	flag.StringVar(&cfg.FlakeNATSCredentialsFile, "flake.nats.credentials-file", "", "NATS credentials file (optional)")
+	flag.StringVar(&cfg.FlakeNATSNkeySeedFile, "flake.nats.nkey-seed-file", "", "NATS NKey seed file (optional)")
 
 	flag.Parse()
 

main.go

@@ -15,7 +15,7 @@ import (
 	"github.com/prometheus/client_golang/prometheus/promhttp"
 )
 
-const version = "0.3.0"
+const version = "0.4.0"
 
 func main() {
 	cfg, err := config.Parse()
@@ -40,6 +40,7 @@ func main() {
 			NATSURL:             cfg.FlakeNATSURL,
 			NATSSubject:         cfg.FlakeNATSSubject,
 			NATSCredentialsFile: cfg.FlakeNATSCredentialsFile,
+			NATSNkeySeedFile:    cfg.FlakeNATSNkeySeedFile,
 		})
 		if err != nil {
 			slog.Error("Failed to create flake collector", "error", err)

module.nix

@@ -58,6 +58,12 @@ in
           default = null;
           description = "Path to NATS credentials file.";
         };
+
+        nkeySeedFile = lib.mkOption {
+          type = lib.types.nullOr lib.types.path;
+          default = null;
+          description = "Path to NATS NKey seed file.";
+        };
       };
     };
 
@@ -133,6 +139,8 @@ in
           "--flake.nats.subject=${cfg.flake.nats.subject}"
         ] ++ lib.optionals (cfg.flake.nats.enable && cfg.flake.nats.credentialsFile != null) [
           "--flake.nats.credentials-file=${cfg.flake.nats.credentialsFile}"
+        ] ++ lib.optionals (cfg.flake.nats.enable && cfg.flake.nats.nkeySeedFile != null) [
+          "--flake.nats.nkey-seed-file=${cfg.flake.nats.nkeySeedFile}"
         ]);
         Restart = "on-failure";
         RestartSec = "5s";