Refactor environment variable handling in main.go

- Updated command-line flag definitions to use a helper function for retrieving environment variables, allowing for more flexible configuration.
- Changed default values for Gitea server URL, config path, UA blocklist path, and server port to be set via environment variables.
- Modified CORS middleware to accept allowed origins from an environment variable, enhancing security and configurability.

main.go

@@ -37,10 +37,10 @@ var (
 
 func main() {
 	flag.StringVar(&giteaToken, "t", os.Getenv("GITEA_TOKEN"), "Gitea API Token")
-	flag.StringVar(&giteaServer, "s", "https://git.quad4.io", "Gitea Server URL")
-	flag.StringVar(&configPath, "c", config.DefaultConfigPath, "Path to software.txt (local or remote)")
-	uaBlocklistPath := flag.String("ua-blocklist", "ua-blocklist.txt", "Path to ua-blocklist.txt (optional)")
-	port := flag.String("p", "8080", "Server port")
+	flag.StringVar(&giteaServer, "s", getEnv("GITEA_SERVER", "https://git.quad4.io"), "Gitea Server URL")
+	flag.StringVar(&configPath, "c", getEnv("CONFIG_PATH", config.DefaultConfigPath), "Path to software.txt (local or remote)")
+	uaBlocklistPath := flag.String("ua-blocklist", getEnv("UA_BLOCKLIST_PATH", "ua-blocklist.txt"), "Path to ua-blocklist.txt (optional)")
+	port := flag.String("p", getEnv("PORT", "8080"), "Server port")
 	isProd := flag.Bool("prod", os.Getenv("NODE_ENV") == "production", "Run in production mode")
 	updateInterval := flag.Duration("u", 1*time.Hour, "Software update interval")
 	flag.Parse()
@@ -58,8 +58,9 @@ func main() {
 
 	r := chi.NewRouter()
 
+	allowedOrigins := strings.Split(getEnv("ALLOWED_ORIGINS", "*"), ",")
 	r.Use(cors.Handler(cors.Options{
-		AllowedOrigins:   []string{"*"},
+		AllowedOrigins:   allowedOrigins,
 		AllowedMethods:   []string{"GET", "POST", "OPTIONS"},
 		AllowedHeaders:   []string{"Accept", "Authorization", "Content-Type", "X-CSRF-Token", "X-Account-Number"},
 		ExposedHeaders:   []string{"Link"},
@@ -172,3 +173,10 @@ func main() {
 	}
 	fmt.Println("Server exited properly")
 }
+
+func getEnv(key, fallback string) string {
+	if value, ok := os.LookupEnv(key); ok {
+		return value
+	}
+	return fallback
+}