Not possible to alter quiz take access

Problem/Motivation

It's currently not possible for other modules to alter the "take" access for quizzes.

Steps to reproduce

Have a quiz type that all users are allowed to see, but that can only be taken by some users/roles.

Proposed resolution

Require a specific "allowed" access result, and alter quiz_quiz_access() so it does not return a forbidden when a user does not have the "access quiz" permission.

Remaining tasks

User interface changes

API changes

Data model changes