Updated contextKey type declarations

Author: PythonHacker24

api/middleware/model.go

@@ -0,0 +1,10 @@
+package middleware
+
+/* contextKey type for middleware context value passing */
+type contextKey string
+
+/* defining contextKey types */
+const (
+	ContextKeyUsername  contextKey = "username"
+	ContextKeySessionID contextKey = "session_id"
+)