Add JWT configuration and implement token generation in Steam login callback

src/etc/authenticator.yaml

@@ -6,6 +6,11 @@ Steam:
   CallbackURL: https://www.cialloo.com/api/authenticator/steam/callback
   FrontendCallbackURL: https://www.cialloo.com/auth/callback
 
+JWT:
+  Secret: your-secret-key-change-in-production
+  Issuer: cialloo-authenticator
+  ExpiresIn: 604800  # 7 days in seconds
+
 Redis:
   Host: redis.production.svc.cluster.local:6379
   Type: node