[FC-0118] docs: add ADR for standardizing authentication patterns

docs/decisions/0034-unify-auth-oauth2-dot-v2.rst

@@ -0,0 +1,151 @@
+Standardize Authentication Patterns and Security Schemes
+========================================================
+
+:Status: Proposed
+:Date: 2026-04-07
+:Deciders: Open edX Platform / API Working Group
+:Technical Story: Open edX REST API Standards - Consistent authentication patterns and security scheme usage
+
+Context
+=======
+
+Open edX APIs have inconsistent authentication patterns and security scheme implementations:
+
+* Some APIs use OAuth2, others use JWT, some use session authentication
+* Multiple authentication mechanisms are enabled globally but not consistently applied
+* Security scheme declarations don't match actual authentication behavior
+* External integrators cannot reliably predict which authentication method to use
+* Internal APIs mix authentication mechanisms without clear patterns
+
+This inconsistency creates confusion for:
+- External developers determining which auth method to implement
+- Internal teams maintaining consistent authentication patterns
+- Security reviews and compliance assessments
+- Automated tools expecting predictable authentication
+
+Decision
+========
+
+1. **OAuth2 via Django OAuth Toolkit (DOT) MUST be the standard authentication
+   mechanism for external API access**
+2. **JWT authentication MUST be used only for internal service-to-service communication**
+3. **Session authentication MUST be used only for browser-based UI interactions**
+4. **All new APIs MUST follow these authentication patterns based on use case**
+5. **Existing APIs MUST be audited and updated to follow consistent patterns**
+
+Implementation requirements:
+
+* External APIs (public, partner integrations): OAuth2 only
+* Internal APIs (service-to-service): JWT only  
+* Browser-based APIs (UI interactions): Session only
+* DRF authentication classes must match the intended use case
+* No mixing of authentication mechanisms in single endpoints
+
+Consequences
+============
+
+* Pros
+
+  * Clear, predictable authentication patterns for different API use cases
+  * Improved security through proper separation of auth mechanisms
+  * Easier integration for external developers (OAuth2 standard)
+  * Simplified internal service communication (JWT)
+  * Better browser experience (session-based auth)
+
+* Cons / Costs
+
+  * Existing APIs need audit and potential refactoring to match patterns
+  * Teams need to understand and implement proper authentication choices
+  * Some APIs may need to be split or redesigned for single auth mechanism
+  * Migration effort for services currently using mixed authentication
+
+Relevance in edx-platform
+=========================
+
+* **OAuth2/DOT**: LMS uses Django OAuth Toolkit at ``/oauth2/``
+  (``lms/urls.py``, ``openedx/core/djangoapps/oauth_dispatch``). Settings include
+  ``OAUTH2_PROVIDER_APPLICATION_MODEL``, ``OAUTH2_VALIDATOR_CLASS`` (e.g.
+  ``EdxOAuth2Validator``).
+* **Current API auth**: ``openedx/core/lib/api/view_utils.view_auth_classes``
+  configures both **JWT** and **OAuth2** (Bearer) and session:
+
+  .. code-block:: python
+
+     # openedx/core/lib/api/view_utils.py (current)
+     func_or_class.authentication_classes = (
+         JwtAuthentication,
+         BearerAuthenticationAllowInactiveUser,  # OAuth2 Bearer via DOT
+         SessionAuthenticationAllowInactiveUser
+     )
+
+* **Bearer auth**: ``openedx/core/lib/api/authentication.py`` implements
+  ``BearerAuthentication`` / ``BearerAuthenticationAllowInactiveUser`` using
+  ``oauth2_provider`` (DOT) for access token validation.
+
+Code examples (authentication patterns by use case)
+===================================================
+
+* **External API (OAuth2 only):**
+
+.. code-block:: python
+
+   from rest_framework import viewsets
+   from openedx.core.lib.api.authentication import BearerAuthenticationAllowInactiveUser
+   from rest_framework.permissions import IsAuthenticated
+
+   class ExternalCourseViewSet(viewsets.ViewSet):
+       """External API for course data - OAuth2 authentication only."""
+       authentication_classes = [BearerAuthenticationAllowInactiveUser]
+       permission_classes = [IsAuthenticated]
+
+* **Internal Service API (JWT only):**
+
+.. code-block:: python
+
+   from rest_framework import viewsets
+   from openedx.core.lib.api.authentication import JwtAuthentication
+   from rest_framework.permissions import IsAuthenticated
+
+   class InternalServiceViewSet(viewsets.ViewSet):
+       """Internal service-to-service API - JWT authentication only."""
+       authentication_classes = [JwtAuthentication]
+       permission_classes = [IsAuthenticated]
+
+* **Browser-based API (Session only):**
+
+.. code-block:: python
+
+   from rest_framework import viewsets
+   from openedx.core.lib.api.authentication import SessionAuthenticationAllowInactiveUser
+   from rest_framework.permissions import IsAuthenticated
+
+   class BrowserUIViewSet(viewsets.ViewSet):
+       """Browser UI API - Session authentication only."""
+       authentication_classes = [SessionAuthenticationAllowInactiveUser]
+       permission_classes = [IsAuthenticated]
+
+Implementation Notes
+====================
+
+* Audit existing APIs to identify authentication pattern violations
+* Create guidelines for determining appropriate authentication mechanism
+* Update global authentication configurations to enforce patterns
+* Provide migration guidance for APIs currently using mixed authentication
+* Document authentication patterns for development teams
+
+Rollout Plan
+------------
+
+1. Audit existing APIs and categorize by intended use case (external/internal/browser)
+2. Update global authentication configurations to prevent mixed authentication
+3. Refactor high-priority APIs to follow single-authentication patterns
+4. Create development guidelines and documentation for authentication choices
+5. Implement automated testing to validate authentication pattern compliance
+6. Monitor and enforce authentication patterns in code reviews
+
+References
+==========
+
+* Django REST Framework - Authentication and permissions
+* Django OAuth Toolkit documentation
+* Open edX Authentication Patterns Guide