Merge branch 'variable-refactor' into 'main'

...end/main/java/edu/ntnu/idatt2105/QuizCreationAndTest.java

...u/ntnu/idatt2105/configuration/SecurityConfiguration.java

...u/ntnu/idatt2105/controller/AuthenticationController.java

...nd/main/java/edu/ntnu/idatt2105/dto/LoginResponseDTO.java

...src/backend/main/java/edu/ntnu/idatt2105/dto/UserDTO.java

...main/java/edu/ntnu/idatt2105/dto/UserRegistrationDTO.java

.../src/backend/main/java/edu/ntnu/idatt2105/model/User.java

...in/java/edu/ntnu/idatt2105/repository/UserRepository.java

...ava/edu/ntnu/idatt2105/service/AuthenticationService.java

...nd/main/java/edu/ntnu/idatt2105/service/TokenService.java

...end/main/java/edu/ntnu/idatt2105/service/UserService.java