Refactor AuthService for better error handling and CRUD usage

Replaced raw database queries with CRUD operations for consistency and modularity. Enhanced error handling by adding detailed exception messages and logging for failed actions, such as authentication and registration. Updated tests to reflect new exception-based error handling approach.

backend/tests/services/test_auth_service.py

@@ -32,13 +32,14 @@ class TestAuthServiceAuthentication:
 
     def test_authenticate_nonexistent_user(self, db_session):
         """Test authenticating with an email that doesn't exist"""
-        user = AuthService.authenticate_user(
-            db=db_session,
-            email="nonexistent@example.com",
-            password="password"
-        )
+        with pytest.raises(AuthenticationError):
+            user = AuthService.authenticate_user(
+                db=db_session,
+                email="nonexistent@example.com",
+                password="password"
+            )
 
-        assert user is None
+            assert user is None
 
     def test_authenticate_with_wrong_password(self, db_session, mock_user):
         """Test authenticating with the wrong password"""
@@ -48,13 +49,14 @@ class TestAuthServiceAuthentication:
         db_session.commit()
 
         # Authenticate with wrong password
-        user = AuthService.authenticate_user(
-            db=db_session,
-            email=mock_user.email,
-            password="WrongPassword123"
-        )
+        with pytest.raises(AuthenticationError):
+            user = AuthService.authenticate_user(
+                db=db_session,
+                email=mock_user.email,
+                password="WrongPassword123"
+            )
 
-        assert user is None
+            assert user is None
 
     def test_authenticate_inactive_user(self, db_session, mock_user):
         """Test authenticating an inactive user"""