switch from client_secret to client_secret_file

README.md

@@ -43,7 +43,7 @@ Create `$XDG_CONFIG_HOME/nix-cache-login/config.toml` (default `~/.config/nix-ca
 ```toml
 issuer = "https://id.guardianproject.info/realms/gp"
 client_id = "nix-cache"
-cache_host = "cache.guardianproject.info"
+cache_host = "cache.guardianproject.dev"
 netrc_path = "$XDG_CONFIG_HOME/nix/netrc"
 ```
 
@@ -51,8 +51,8 @@ netrc_path = "$XDG_CONFIG_HOME/nix/netrc"
 ```toml
 issuer = "https://id.guardianproject.info/realms/gp"
 client_id = "nix-cache-server"
-client_secret = "..."
-cache_host = "cache.guardianproject.info"
+client_secret_file = "/run/secrets/nix-cache-client-secret"
+cache_host = "cache.guardianproject.dev"
 netrc_path = "$XDG_CONFIG_HOME/nix/netrc"
 ```
 

cmd/serviceAccount.go

@@ -18,7 +18,7 @@ var serviceAccountCmd = &cobra.Command{
 	Use:   "service-account",
 	Short: "Authenticate using client credentials (for servers)",
 	Long: `Authenticates using the OAuth2 client credentials flow for headless
-server environments. Requires client_secret in the config file.
+server environments. Requires client_secret_file in the config file.
 Exits 0 on success, 1 on failure. Designed to be called from a systemd timer.`,
 	RunE: runServiceAccount,
 }
@@ -31,7 +31,7 @@ func runServiceAccount(cmd *cobra.Command, args []string) error {
 	ctx := context.Background()
 
 	if cfg.ClientSecret == "" {
-		fmt.Fprintln(os.Stderr, "Error: client_secret is required in config for service-account mode.")
+		fmt.Fprintln(os.Stderr, "Error: client_secret_file is required in config for service-account mode.")
 		os.Exit(1)
 	}
 

internal/config/config.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
+	"strings"
 
 	"github.com/adrg/xdg"
 	toml "github.com/pelletier/go-toml/v2"
@@ -12,9 +13,12 @@ import (
 type Config struct {
 	Issuer           string `toml:"issuer"`
 	ClientID         string `toml:"client_id"`
-	ClientSecret string `toml:"client_secret,omitempty"`
+	ClientSecretFile string `toml:"client_secret_file,omitempty"`
 	CacheHost        string `toml:"cache_host"`
 	NetrcPath        string `toml:"netrc_path"`
+
+	// ClientSecret is populated at load time by reading ClientSecretFile.
+	ClientSecret string `toml:"-"`
 }
 
 // Load reads the config from the given path, or from the default XDG location.
@@ -34,6 +38,15 @@ func Load(path string) (*Config, error) {
 	}
 
 	cfg.NetrcPath = os.ExpandEnv(cfg.NetrcPath)
+	cfg.ClientSecretFile = os.ExpandEnv(cfg.ClientSecretFile)
+
+	if cfg.ClientSecretFile != "" {
+		secret, err := os.ReadFile(cfg.ClientSecretFile)
+		if err != nil {
+			return nil, fmt.Errorf("reading client_secret_file: %w", err)
+		}
+		cfg.ClientSecret = strings.TrimSpace(string(secret))
+	}
 
 	if err := cfg.validate(); err != nil {
 		return nil, err

internal/config/config_test.go

@@ -39,14 +39,19 @@ netrc_path = "/home/user/.config/nix/netrc"
 	}
 }
 
-func TestLoadConfigWithClientSecret(t *testing.T) {
+func TestLoadConfigWithClientSecretFile(t *testing.T) {
 	dir := t.TempDir()
 	cfgFile := filepath.Join(dir, "config.toml")
+	secretFile := filepath.Join(dir, "secret")
+
+	if err := os.WriteFile(secretFile, []byte("super-secret\n"), 0600); err != nil {
+		t.Fatal(err)
+	}
 
 	content := `
 issuer = "https://id.example.com/realms/test"
 client_id = "nix-cache-server"
-client_secret = "super-secret"
+client_secret_file = "` + secretFile + `"
 cache_host = "cache.example.com"
 netrc_path = "/tmp/netrc"
 `
@@ -64,6 +69,30 @@ netrc_path = "/tmp/netrc"
 	}
 }
 
+func TestLoadConfigClientSecretFileMissing(t *testing.T) {
+	dir := t.TempDir()
+	cfgFile := filepath.Join(dir, "config.toml")
+
+	content := `
+issuer = "https://id.example.com/realms/test"
+client_id = "nix-cache-server"
+client_secret_file = "/nonexistent/secret"
+cache_host = "cache.example.com"
+netrc_path = "/tmp/netrc"
+`
+	if err := os.WriteFile(cfgFile, []byte(content), 0644); err != nil {
+		t.Fatal(err)
+	}
+
+	_, err := Load(cfgFile)
+	if err == nil {
+		t.Fatal("expected error, got nil")
+	}
+	if !contains(err.Error(), "client_secret_file") {
+		t.Errorf("error = %q, want to contain %q", err.Error(), "client_secret_file")
+	}
+}
+
 func TestEnvVarExpansionInNetrcPath(t *testing.T) {
 	dir := t.TempDir()
 	cfgFile := filepath.Join(dir, "config.toml")