[BD-24][TNL-7919] LTI Advantage Names and Roles provisioning service...

[BD-24][TNL-7919] LTI Advantage Names and Roles provisioning service implementation direction (#142)

* Add wip ADR about NRPS

* Nit

* Update docs/decisions/0004-lti-advantage-nrps.rst

Co-authored-by: Ned Batchelder <ned@nedbatchelder.com>

* Update docs/decisions/0004-lti-advantage-nrps.rst

Co-authored-by: Ned Batchelder <ned@nedbatchelder.com>

* Address nits

* Write a bit more

* Update docs/decisions/0004-lti-advantage-nrps.rst

Co-authored-by: Ned Batchelder <ned@nedbatchelder.com>

* Update docs/decisions/0004-lti-advantage-nrps.rst

Co-authored-by: Ned Batchelder <ned@nedbatchelder.com>

* Update docs/decisions/0004-lti-advantage-nrps.rst

Co-authored-by: Ned Batchelder <ned@nedbatchelder.com>

* Update docs/decisions/0004-lti-advantage-nrps.rst

Co-authored-by: Ned Batchelder <ned@nedbatchelder.com>

* Update docs/decisions/0004-lti-advantage-nrps.rst

Co-authored-by: Ned Batchelder <ned@nedbatchelder.com>

* Nits

Co-authored-by: Ned Batchelder <ned@nedbatchelder.com>

docs/decisions/0004-lti-advantage-nrps.rst

+LTI Advantage NRPS (Names and Roles provisioning services)
+----------------------------------------------------------
+
+Status
+======
+
+Accepted
+
+Context
+=======
+
+One of the LTI Advantage services is the `Names and Roles Provisioning Services (NRPS)`_, which allows LTI tools
+to retrieve a user list associated with the learning context and internally provision resources for them.
+
+From the LTI-NRPS Specification:
+
+    The Names and Role Provisioning Services is based on IMS Learning Information Services (LIS) [LIS-20]
+    and W3C Organization Ontology [W3C-ORG]. It is concerned with providing access to data about users’ roles
+    within organizations, a course being an example of an organization. So a very common purpose for this service
+    is to provide a roster (list of enrolments) for a course.
+
+An LTI-NRPS services implementation consists of two services which provide user data in the following format:
+
+.. code-block:: json
+    {
+        "id" : "https://lms.example.com/sections/2923/memberships",
+        "context": {
+            "id": "2923-abc",
+            "label": "CPS 435",
+            "title": "CPS 435 Learning Analytics",
+        },
+        "members" : [
+            {
+                "status" : "Active",
+                "name": "Jane Q. Public",
+                "picture" : "https://platform.example.edu/jane.jpg",
+                "given_name" : "Jane",
+                "family_name" : "Doe",
+                "middle_name" : "Marie",
+                "email": "jane@platform.example.edu",
+                "user_id" : "0ae836b9-7fc9-4060-006f-27b2066ac545",
+                "lis_person_sourcedid": "59254-6782-12ab",
+                "roles": [
+                    "http://purl.imsglobal.org/vocab/lis/v2/membership#Instructor"
+                ]
+            }
+        ]
+    }
+
+Where the only required fields for each member are :code:`user_id` and :code:`roles`, to avoid unintended PII transmission to a third party.
+But since one of the purposes of this API is to enable tools access to user PII, the implementation should provide a flag to enable the consumer
+to pass additional PII parameters such as name, email, and a profile picture url.
+
+The main issue with enabling this API (`even with pagination as defined in the spec`_) is that it would allow external third-party tools to scrape enrollments for all
+students in a given course. Given the scale of some courses in edX.org, even if the API is made more performant with cursor pagination,
+we're still left with an API pattern that would be actively encouraging clients out there to make hundreds of thousands of successive requests in order
+to crawl enrollment data.
+
+.. _Names and Roles Provisioning Services (NRPS): http://www.imsglobal.org/spec/lti-nrps/v2p0
+.. _even with pagination as defined in the spec: http://www.imsglobal.org/spec/lti-nrps/v2p0#limit-query-parameter
+
+Decision
+========
+
+Implement the LTI NRPS for courses up to a predefined (and configurable) number of active enrollments.
+Above that number, the service endpoint will return HTTP status 403 (Forbidden).
+
+This is the simplest implementation that allows us to provide the LTI NRPS service and mitigate the concerns mentioned above.
+The NRPS services availability and behavior will be controlled by the following toggles:
+
+.. list-table::
+   :widths: auto
+   :header-rows: 1
+
+   * - Toggle name
+     - Type
+     - Behavior
+   * - LTI_NRPS_ENABLED
+     - Feature flag
+     - Enables and disables LTI NRPS globally in the Open edX instance. Is disabled by default.
+   * - LTI_NRPS_ACTIVE_ENROLLMENT_LIMIT
+     - Django setting
+     - Controls the allowed number of active enrollments when the API is enabled.
+       Defaults to 1000 active enrollments at first.
+   * - LTI_NRPS_TRANSMIT_PII
+     - CourseWaffleFlag
+     - Allows the tool to access student and instructor PII (username, email, full name, profile picture).
+       Defaults to False.
+
+
+Consequences
+============
+
+* Small courses will be able to use LTI NRPS endpoints on their tools, up to a limited amount of users.
+* Big MOOCs (with millions of users) won't allow scraping of enrollment data on edX and potentially cause stability issues.
+
+
+Discarded solutions
+===================
+
+Don't implement NRPS
+~~~~~~~~~~~~~~~~~~~~
+This would not enable course creators to use LTI advantage tools that make use of this functionality.
+
+Implement NRPS gated by course
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+While this would work, it adds a maintenance burden of keeping and updating a whitelist.
+Also, long running MOOCs can grow to sizes that could potentially affect instance stability when
+using the API.
+
+Implement NRPS limiting the context of the data retrieved
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Complex to implement given the benefit. To get consistency on the LTI tool side, the implementation
+would need to create user groups and effectively isolate them in the tool (potentially using a different resourceLink),
+which doesn't work for a few LTI integrations (forums, course wide leaderboard, instructor grading inside the tool and others).