def _validate_signup_data(self, study, email, username, password):
        errors = []
        if not study:
            errors.append("Missing study value")
        if not email:
            errors.append("Missing email value")
        if not username:
            errors.append("Missing username value")
        else:
            user_dao = UserDAO()
            users = user_dao.get_user_by_username(username)
            if users:
                errors.append("username taken")
        if not password:
            errors.append("Missing password value")

        if errors:
            raise AuthorizationServiceException(errors.join(", "))