feat: Add authentication middleware to charging-engine with public and protected route separation

- Add auth module import to main.rs
- Add AuthConfig initialization from environment in main function
- Add auth_config field to AppState struct
- Add auth_middleware layer to protected routes
- Move health check, credit check, deduct, balance, and usage recording to public routes (no auth required for packet-gateway integration)
- Move add credit, subscriber management, rating plans, monitoring, and engine

apps/charging-engine/src/main.rs

@@ -1,3 +1,4 @@
+mod auth;
 mod charging;
 mod monitoring;
 mod errors;
@@ -11,6 +12,7 @@ use tracing::info;
 
 use routes::create_router;
 use charging::{ChargingEngine, RatingPlansRepo};
+use auth::AuthConfig;
 
 #[tokio::main]
 async fn main() -> Result<()> {
@@ -44,8 +46,10 @@ async fn main() -> Result<()> {
     info!("Connected to Redis successfully");
 
     // Create application state
+    let auth_config = AuthConfig::from_env();
     let state = crate::models::AppState {
         charging_engine,
+        auth_config,
     };
 
     // Create router