Merge pull request #85 from open-craft/giovanni/bb-2612-lti-implementation-adr

[BD-2] [BB-2612]: Add ADR to define LTI Plugin architecture implementation

docs/decisions/0001-lti-extensions-plugin.rst

+Platform wide LTI support
+----------------------------
+
+Status
+======
+
+Accepted
+
+Context
+=======
+
+The LTI Consumer implementation in the Open edX platform is currently limited to LTI launches inside XBlocks.
+
+The goal of this ADR is to:
+
+#. Define an architecture to enable LTI launch and configuration for multiple contexts (from block level to platform level).
+#. Make LTI configuration reusable throughout a context.
+#. Support both LTI 1.1 and LTI 1.3, as well as LTI Advantage.
+
+Decisions
+=========
+
+Develop LTI related code to be reusable in the platform context, and allow LTI to be configured for different contexts in the platform.
+This requires adding a separation layer between the framework presenting the content and the LTI logic, configuration and storage layer.
+
+The first steps were already taken to move towards this implementation with these PRs:
+
+`Merge LTI 1.3 support to master`_: Implemented support for LTI 1.3 by creating a framework agnostic python module that handles the
+LTI specific logic (such as launch message creation, token verification and OIDC flows) and passing responses as JSON objects to be
+interpreted and presented by the XBlock LTI consumer.
+The module is easily reusable in contexts outside the XBlock and all the code in `lti_consumer/lti_1p3` don't rely on XBlock or
+Django specific features.
+The PR uses the XBlock's fields to store LTI configuration.
+
+`Add support for LTI embeds in course tabs and elsewhere`_: This is a partial implementation of logic separation for the LTI 1.1
+consumer to allow LTI launches from outside the context of an XBlock, following the guidelines set by the LTI 1.3 implementation.
+While this is a smaller step than the implementation above, it allows LTI 1.1 launches on any LMS/Studio view, but doesn't implement
+the configuration storage.
+
+.. _`Merge LTI 1.3 support to master`: https://github.com/edx/xblock-lti-consumer/pull/82
+.. _`Add support for LTI embeds in course tabs and elsewhere`: https://github.com/edx/xblock-lti-consumer/pull/77
+
+
+A few actions that need to be taken to achieve the desired architecture are outlined below:
+
+Centralized configuration for LTI launches
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Use Django models to store LTI related configuration and launch data for all LTI integrations.
+This will provide a consistent configuration store throughout the platform and a single point of
+maintenance and development for LTI related features (good since the LTI Specification is well defined).
+
+Additionaly this would include configurations UI on Studio (to enable setup by instructors) and
+also through Django Admin (enable for larger contexts: programs or platform-wide).
+
+
+New LTI Python API
+~~~~~~~~~~~~~~~~~~
+
+A new Python API needs to be developed to provide LTI support platform wide.
+This API should provide methods to configure, modify and perform LTI launches
+from multiple platform contexts (Django, XBlocks).
+
+A centralized launch & configuration API will make LTI integration consistent
+across all platform's contexts.
+
+Change folder structure and rename repository
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+To better reflect the new repo usage, rename the repository to "openedx-lti-consumer" and
+change the folder structure.
+
+Here is the new proposed folder structure::
+  # Django plugabble app main folder
+  lti_consumer/
+
+  # Python APIs - following `Inter App APIs`_ guidelines
+  lti_consumer/api.py
+
+  # LTI specific logic (no storage)
+  lti_consumer/lti_1p1
+  lti_consumer/lti_1p3
+
+  # LTI Configuration, launch and services storage
+  lti_consumer/models/
+
+  # Pluggable extensions points that can be used in the platform
+  lti_consumer/extensions/
+  lti_consumer/extensions/xblock.py  # To replace current XBlock LTI Consumer, can use course import/export hooks to change settings
+  lti_consumer/extensions/django.py  # To easily enable LTI embeds anywhere in the platform
+  lti_consumer/extensions/course_tab.py  # Inherit Django extension above and add helpers to use course context for a few use cases (forum tab, course embed)
+
+
+:: _`Inter App APIs`: https://github.com/edx/edx-platform/blob/master/docs/decisions/0002-inter-app-apis.rst
+
+Tech Debt
+=========
+
+The current LTI implementation stores launch configuration and user data in XBlock Settings fields.
+We'll need a transition phase and a migration path before fully deprecating the old configuration storage.
+
+The transition phase can allow configuring LTI integration both locally (on the XBlock) and using the
+generic configuration.
+
+
+Consequences
+============
+
+* LTI configuration will be independent from courses, so secret keys, access tokens and general LTI launch configuration won't
+  be carried over when importing/exporting courses for security purposes. LTI Tools need to be reconfigured or use contexts available
+  whitin the course/organization.
+
+* The LTI consumer will use Django models to store launch configuration (being a plugin, that's already possible).
+
+* Enables LTI integration throughout the platform, without limitations of XBlocks and even outside a course context.
\ No newline at end of file