Add ADRs for FBE decisions

REVMI-39

openedx/features/content_type_gating/docs/decisions/0001-group-access-overrides.rst

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+1. Group Access Overrides
+=========================
+
+Status
+------
+
+Accepted
+
+Context
+-------
+
+In order to implement Feature Based Enrollment (FBE), we need to be able
+to automatically restrict content to a specific set of authorized
+users. This automatic restriction needs to be based on whether content
+is graded and capable of producing a score. Whether a particular XBlock
+is graded and scorable is denoted by attributes on that XBlock.
+
+There are two separate systems that need load XBlocks and need to
+be restricted: the courseware rendering on the web, and the courseware
+rendering in the mobile app. Courseware rendering accesses XBlock
+attributes via the ``FieldData`` api, and can be modified by
+``FieldDataOverrides``. The mobile app uses the course_blocks api,
+which is backed by ``BlockTransformers``.
+
+Most differentiated content is managed by ``UserPartitions``. These
+segment users by customizable criteria, and then can be applied as
+access control by setting the ``group_access`` field on an ``XBlock``.
+There is an existing ``UserPartition`` that segments users based on
+their enrollment track (the ``EnrollmentTrackUserPartition``. However,
+many courses already manage content using the ``EnrollmentTrackUserPartition``,
+so it isn't a good candidate to overwrite for FBE.
+
+
+Decision
+--------
+
+In order to restrict access to graded content, we will create a new
+``UserPartition`` specifically for FBE. That partition will segment
+users based on their enrollment track and any other criteria that become
+relevant for FBE implementation. We will override the ``group_access``
+of all graded and scorable XBlocks by using a new ``FieldDataOverride``
+for in-courseware acccess, and a new ``BlockTransformer`` for mobile/
+course_blocks api access. Both of those will respect the same rules for
+when to override the ``group_access`` attribute.
+
+Consequences
+------------
+
+All graded content (with possible manual exceptions) will have ``group_access``
+overridden to assign the content to the "Full Access Only" partition of
+the new ``ContentTypeGatingPartition``. Studio Authors will see reference
+to both the ``ContentTypeGatingPartition`` (Feature Based Enrollment Partition)
+and the ``EnrollmentTrack`` partition in Studio, if they are authorized to
+modify them. Masquerade, which only modifies a single group at a time, is
+unable to provide an accurate simulation of the interaction between having
+graded content restricted behind the ``EnrollmentTrack`` partition.

openedx/features/content_type_gating/docs/decisions/0002-no-new-track.rst

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+2. No New Enrollment Mode
+=========================
+
+Status
+------
+
+Accepted
+
+Context
+-------
+
+In order to implement Feature Based Enrollment (FBE), we need a way
+to differentiate between users who have access to graded content
+and those who don't. We need to be able to move users between those
+groups. Users that have access to graded content should also get
+all of the current behavior associated with Verified users. We
+need to leave existing users (in any track) with their existing behavior.
+Many permissions related to Enrollment Modes are checked by checking
+whether an enrollment has a specific mode, which makes it hard
+to add a new mode that has the same set of permissions.
+
+
+Decision
+--------
+
+Rather than adding a new Enrollment Track that we move Full-Access users
+into, we will add a new ``UserPartition`` to distinguish Limited-Access Users
+and Full-Access Users.
+
+Consequences
+------------
+
+Some Studio Authors see both the new ``ContentTypeGatingPartition`` and the
+``EnrollmentTrackUserPartition`` in their UI. Masquerade is unable to
+masquerade as a user in a specific group and see graded content that has
+been limited using the ``EnrollemntTrackUserPartition``, because it doesn't
+multi-select groups.

openedx/features/course_duration_limits/docs/decisions/0001-access-messages.rst

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+1. Pre-formatted Access Messages
+================================
+
+Status
+------
+
+Accepted
+
+Context
+-------
+
+In ``course_duration_limits``, we are adding a new permissions
+state that will restrict the user from entering the course.
+The point at which this condition is checked is deep within
+edx-platform, but the error message needs to display at the
+surface of the application. In order to preserve information
+display consistency, we want to receive the error message
+in the UI in a standard format. We can use ``AccessResponse.user_message``
+to store that permission-specific error message. However,
+different pages require more or less context. In particular,
+when displaying an access error message inside the courseware,
+we don't need to specify the current course, but when displaying
+the same message on the course dashboard, we do.
+
+Decision
+--------
+
+We will add a field to ``AccessResponse``, ``additional_context_user_message``,
+which will be used in non-course-specific contexts (for
+``course_duration_limits``. The name is non-specific in order to enable it
+to be used more generally by other access-control schemes that might have
+different levels of context display needs.
+
+Consequences
+------------
+
+``AccessResponse`` messages can be more detailed, and more specific
+to the required context. The additional attribute on ``AccessResponse``
+is somewhat vague, and potentially confusing to a new reader. Which additional
+context is relevant is not specified, so if we need more or different
+context (rather than just course-context), we will need to rework the
+current system or add more attributes.
+