(backend) wip introduce a token exchange endpoint

src/backend/core/api/feature_flag.py

@@ -16,6 +16,7 @@ class FeatureFlag:
         "file_upload": "FILE_UPLOAD_ENABLED",
         "addons": "ADDONS_ENABLED",
         "application": "APPLICATION_ENABLED",
+        "user_access_token": "USER_ACCESS_TOKEN_ENABLED",
     }
 
     @classmethod

src/backend/core/api/serializers.py

@@ -580,3 +580,25 @@ class ExternalProcessEventSerializer(BaseValidationOnlySerializer):
     # useless bad requests
     type = serializers.CharField(required=False, allow_null=True, allow_blank=True)
     status = serializers.CharField(required=False, allow_null=True, allow_blank=True)
+
+
+class TransitCodeSerializer(BaseValidationOnlySerializer):
+    """Validate the single-use transit code sent to the exchange endpoint."""
+
+    # todo if I can pass the max length directly to the char field
+    code = serializers.CharField(max_length=255, trim_whitespace=True)
+
+    def validate_code(self, value):
+        """Reject codes whose length cannot match a generated one.
+
+        `secrets.token_urlsafe(nbytes)` produces (4 * nbytes + 2) // 3
+        url-safe characters. Checking the length against the configured
+        TRANSIT_CODE_NBYTES makes malformed codes fail fast with a 400,
+        before any cache lookup.
+        """
+        expected_length = (4 * settings.TRANSIT_CODE_NBYTES + 2) // 3
+
+        if len(value) != expected_length:
+            raise serializers.ValidationError("Invalid transit code format.")
+
+        return value

src/backend/core/api/throttling.py

@@ -73,3 +73,14 @@ class CreationCallbackAnonRateThrottle(MonitoredAnonRateThrottle):
     """Throttle Anonymous user requesting room generation callback"""
 
     scope = "creation_callback"
+
+
+class ExchangeAccessTokenAnonRateThrottle(MonitoredAnonRateThrottle):
+    """Throttle anonymous transit code exchange attempts.
+
+    Abuse mitigation only, not a security boundary: DRF throttling is
+    best-effort. The security of the exchange rests on the codes'
+    entropy and single use.
+    """
+
+    scope = "exchange_access_token"

src/backend/core/api/viewsets.py

@@ -69,6 +69,7 @@ from core.recording.worker.mediator import (
     WorkerServiceMediator,
 )
 from core.services.invitation import InvitationService
+from core.services.jwt_token import JwtTokenService
 from core.services.livekit_events import (
     LiveKitEventsService,
     LiveKitWebhookError,
@@ -93,6 +94,7 @@ from core.services.room_roles import (
     RoomRoleService,
 )
 from core.services.subtitle import SubtitleException, SubtitleService
+from core.services.transit_code import TransitCodeService
 from core.tasks.file import process_file_deletion
 
 from ..authentication.livekit import LiveKitTokenAuthentication
@@ -229,6 +231,76 @@ class UserViewSet(
             self.serializer_class(request.user, context=context).data
         )
 
+    @decorators.action(
+        detail=False,
+        methods=["post"],
+        url_path="exchange-access-token",
+        permission_classes=[],
+        throttle_classes=[throttling.ExchangeAccessTokenAnonRateThrottle],
+    )
+    @FeatureFlag.require("user_access_token")
+    def exchange_access_token(self, request):
+        """Exchange a single-use transit code for a user access token.
+
+        The endpoint is unauthenticated: the transit code itself, an opaque
+        random string obtained through the external API and delivered to
+        the embedded frontend via a URL fragment, is the credential. Each
+        code can be exchanged exactly once (consuming it deletes it from
+        the cache); replaying a consumed code is denied and logged.
+
+        The issued JWT authenticates the user the code was minted for on
+        the whole core API, exactly like a session cookie would (similar
+        to lib-jitsi-meet's token authentication), and never appears in
+        any URL. Role-based permissions apply unchanged.
+        """
+        serializer = serializers.TransitCodeSerializer(data=request.data)
+        serializer.is_valid(raise_exception=True)
+
+        code_data = TransitCodeService().consume_code(serializer.validated_data["code"])
+
+        if code_data is None:
+            logger.warning("Invalid, expired or already used transit code")
+            raise drf_exceptions.PermissionDenied(
+                "Invalid, expired or already used transit code."
+            )
+
+        # Re-check the user at exchange time so that a deactivation after
+        # the transit code was minted is taken into account.
+        try:
+            user = models.User.objects.get(id=code_data["user_id"], is_active=True)
+        except models.User.DoesNotExist as excpt:
+            raise drf_exceptions.PermissionDenied(
+                "This account can no longer access the application."
+            ) from excpt
+
+        token_service = JwtTokenService(
+            secret_key=settings.USER_ACCESS_TOKEN_SECRET_KEY,
+            algorithm=settings.USER_ACCESS_TOKEN_ALG,
+            issuer=settings.USER_ACCESS_TOKEN_ISSUER,
+            audience=settings.USER_ACCESS_TOKEN_AUDIENCE,
+            expiration_seconds=settings.USER_ACCESS_TOKEN_TTL,
+            token_type=settings.USER_ACCESS_TOKEN_TYPE,
+        )
+
+        # todo - discuss wether it's the relevant scope
+        data = token_service.generate_jwt(
+            user,
+            "user:access",
+            {
+                "token_type": "user_access",
+                "client_id": code_data.get("client_id", "unknown"),
+            },
+        )
+
+        # Log for auditing
+        logger.info(
+            "User access token issued from transit code: user_id=%s, client_id=%s",
+            user.id,
+            code_data.get("client_id", "unknown"),
+        )
+
+        return drf_response.Response(data)
+
 
 class RoomViewSet(
     mixins.CreateModelMixin,

src/backend/core/authentication/user_token.py

@@ -0,0 +1,71 @@
+"""User access JWT authentication for the Meet core API.
+
+Allows an embedded frontend (e.g. rendered in an iframe, where third-party
+session cookies are blocked) to authenticate requests on the core API with
+a JWT, obtained by exchanging a single-use transit code (see
+core.services.transit_code and the users exchange-access-token endpoint)
+and passed as a Bearer header. The JWT itself never appears in any URL.
+
+Similar to lib-jitsi-meet's token authentication, the token is bound to a
+user, not to a resource: once authenticated, the request is treated
+exactly like a session-authenticated one, and the existing role-based
+permissions apply unchanged.
+"""
+
+import logging
+
+from django.conf import settings
+
+from rest_framework import exceptions
+
+from core.external_api.authentication import BaseJWTAuthentication
+
+logger = logging.getLogger(__name__)
+
+USER_ACCESS_TOKEN_TYPE_CLAIM = "user_access"  # noqa: S105
+
+
+class UserAccessJWTAuthentication(BaseJWTAuthentication):
+    """JWT authentication for user access tokens.
+
+    Validates user access tokens issued by the users exchange-access-token
+    endpoint and authenticates the user they were issued for. A bearer
+    token that does not verify against the user access token secret is
+    deferred to the next authentication backend; a token that does verify
+    but carries wrong claims is rejected.
+
+    When the feature is disabled (USER_ACCESS_TOKEN_ENABLED=False), the
+    backend is entirely inert: `BaseJWTAuthentication.authenticate`
+    returns None before reading the Authorization header, deferring every
+    request to the next authentication backend.
+    """
+
+    def __init__(self):
+        """Initialize the backend with user access token settings."""
+        super().__init__(
+            secret_key=settings.USER_ACCESS_TOKEN_SECRET_KEY,
+            algorithm=settings.USER_ACCESS_TOKEN_ALG,
+            issuer=settings.USER_ACCESS_TOKEN_ISSUER,
+            audience=settings.USER_ACCESS_TOKEN_AUDIENCE,
+            expiration_seconds=settings.USER_ACCESS_TOKEN_TTL,
+            token_type=settings.USER_ACCESS_TOKEN_TYPE,
+            is_enabled=settings.USER_ACCESS_TOKEN_ENABLED,
+        )
+
+    def validate_payload(self, payload):
+        """Validate the token type and the issuance-audit claim.
+
+        Raises:
+            AuthenticationFailed: If the token verified against the user
+                access token secret but does not carry the expected claims.
+        """
+        if payload.get("token_type") != USER_ACCESS_TOKEN_TYPE_CLAIM:
+            logger.warning("Wrong 'token_type' in user access token payload")
+            raise exceptions.AuthenticationFailed("Invalid token type.")
+
+        # Every token we issue carries the client_id of the application the
+        # transit code was minted for: its absence means the token does not
+        # come from the exchange endpoint.
+        if not payload.get("client_id"):
+            logger.warning("Missing 'client_id' in user access token payload")
+            raise exceptions.AuthenticationFailed("Invalid token claims.")

src/backend/core/external_api/permissions.py

@@ -86,6 +86,14 @@ class HasRequiredRoomScope(BaseScopePermission):
     }
 
 
+class HasRequiredUserScope(BaseScopePermission):
+    """Scope-based permissions for the external user endpoints."""
+
+    scope_map = {
+        "generate_transit_code": models.ApplicationScope.USERS_SESSION,
+    }
+
+
 class RoomPermissions(permissions.BasePermission):
     """Permissions applying to the room API endpoint."""
 

src/backend/core/external_api/viewsets.py

@@ -22,6 +22,7 @@ from rest_framework import (
 from core import analytics, api, models
 from core.api.feature_flag import FeatureFlag
 from core.services.jwt_token import JwtTokenService
+from core.services.transit_code import TransitCodeService
 
 from ..services.provisional_user_service import (
     ProvisionalUserCreationDisabledError,
@@ -218,3 +219,62 @@ class RoomViewSet(
                 "$set": {"email": self.request.user.email},
             },
         )
+
+
+class UserViewSet(viewsets.GenericViewSet):
+    """Application-delegated API for user operations.
+
+    Provides JWT-authenticated access to user operations for external
+    applications acting on behalf of users. All operations are
+    scope-based. Meant to grow with the other user actions exposed to
+    third parties.
+
+    Supported operations:
+    - transit-code: Mint a single-use transit code for the delegated user
+      (requires 'users:session' scope)
+    """
+
+    authentication_classes = [
+        authentication.ApplicationJWTAuthentication,
+        ResourceServerAuthentication,
+    ]
+    permission_classes = [
+        api.permissions.IsAuthenticated & permissions.HasRequiredUserScope
+    ]
+
+    @decorators.action(
+        detail=False,
+        methods=["post"],
+        url_path="transit-code",
+        url_name="transit-code",
+    )
+    @FeatureFlag.require("user_access_token")
+    def generate_transit_code(self, request):
+        """Mint a transit code for the delegated user.
+
+        Returns a short-lived, single-use opaque code to pass to an embedded
+        frontend (e.g. via a URL fragment when cookies are unavailable). The
+        frontend exchanges it once on
+        POST /api/v1.0/users/exchange-access-token/ for a JWT access token,
+        equivalent to session-cookie authentication and never exposed in a URL.
+        """
+        auth_method = type(request.successful_authenticator).__name__
+        client_id = (request.auth or {}).get("client_id", "unknown")
+
+        code = TransitCodeService().create_code(request.user, client_id=client_id)
+
+        # Log for auditing
+        logger.info(
+            "Transit code issued: user_id=%s, client_id=%s, auth_method=%s",
+            request.user.id,
+            client_id,
+            auth_method,
+        )
+
+        return drf_response.Response(
+            {
+                "transit_code": code,
+                "expires_in": settings.TRANSIT_CODE_TTL,
+            },
+            status=drf_status.HTTP_200_OK,
+        )

src/backend/core/migrations/0022_alter_application_scopes.py

@@ -0,0 +1,19 @@
+# Generated by Django 5.2.14 on 2026-07-31 18:27
+
+import django.contrib.postgres.fields
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('core', '0021_recording_external_process_id_alter_recording_status'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='application',
+            name='scopes',
+            field=django.contrib.postgres.fields.ArrayField(base_field=models.CharField(choices=[('rooms:create', 'Create rooms'), ('rooms:list', 'List rooms'), ('rooms:retrieve', 'Retrieve room details'), ('rooms:update', 'Update rooms'), ('rooms:delete', 'Delete rooms'), ('users:session', 'Create user session tokens')], max_length=50), blank=True, default=list, size=None),
+        ),
+    ]

src/backend/core/models.py

@@ -769,6 +769,7 @@ class ApplicationScope(models.TextChoices):
     ROOMS_RETRIEVE = "rooms:retrieve", _("Retrieve room details")
     ROOMS_UPDATE = "rooms:update", _("Update rooms")
     ROOMS_DELETE = "rooms:delete", _("Delete rooms")
+    USERS_SESSION = "users:session", _("Create user session tokens")
 
 
 class Application(BaseModel):

src/backend/core/services/transit_code.py

@@ -0,0 +1,74 @@
+"""Service handling the lifecycle of transit codes.
+
+A transit code is an opaque, cryptographically random, single-use code
+handed to an embedded frontend (through a URL fragment) so it can obtain a
+user access token on the core API without a session cookie. The code
+carries no information by itself: everything it references (user, client)
+is stored server-side in the cache, and consumed atomically on exchange.
+"""
+
+import hashlib
+import secrets
+
+from django.conf import settings
+from django.core.cache import cache
+
+
+class TransitCodeService:
+    """Create and consume single-use transit codes."""
+
+    @staticmethod
+    def _cache_key(code):
+        """Build the cache key for a code.
+
+        The code is hashed so that a dump of the cache never reveals
+        directly usable codes.
+        """
+        digest = hashlib.sha256(code.encode("utf-8")).hexdigest()
+        return f"{settings.TRANSIT_CODE_CACHE_PREFIX}:{digest}"
+
+    def create_code(self, user, client_id="unknown"):
+        """Generate a transit code for a user, and store it.
+
+        The code expires after TRANSIT_CODE_TTL seconds.
+
+        Returns:
+            str: The opaque code to hand to the client.
+        """
+        # Default 48 random bytes -> 64 url-safe characters, 384 bits of
+        # entropy: unguessable and safe to transit through a URL fragment.
+        code = secrets.token_urlsafe(settings.TRANSIT_CODE_NBYTES)
+
+        cache.set(
+            self._cache_key(code),
+            {
+                "user_id": str(user.id),
+                "client_id": client_id,
+            },
+            timeout=settings.TRANSIT_CODE_TTL,
+        )
+
+        return code
+
+    def consume_code(self, code):
+        """Consume a transit code, enforcing single use.
+
+        The code is deleted from the cache upon consumption. `cache.delete`
+        returns whether a key was actually deleted, so if two requests race
+        on the same code, only one of them wins.
+
+        Returns:
+            dict | None: The data stored at creation time ('user_id',
+                'client_id'), or None if the code is unknown, expired or
+                already consumed.
+        """
+        if not code:
+            return None
+
+        key = self._cache_key(code)
+        data = cache.get(key)
+
+        if data is None or not cache.delete(key):
+            return None
+
+        return data

src/backend/core/tests/rooms/test_api_rooms_create.py

@@ -2,9 +2,14 @@
 Test rooms API endpoints in the Meet core app: create.
 """
 
+from datetime import datetime, timedelta, timezone
+
+from django.conf import settings as django_settings
+
 # pylint: disable=redefined-outer-name,unused-argument
 from django.core.cache import cache
 
+import jwt
 import pytest
 from rest_framework.test import APIClient
 
@@ -109,3 +114,38 @@ def test_api_rooms_create_authenticated_existing_slug():
 
     assert response.status_code == 400
     assert response.json() == {"slug": ["Room with this Slug already exists."]}
+
+
+def generate_user_access_token(user):
+    """Generate a valid user access JWT signed with the token secret."""
+    now = datetime.now(timezone.utc)
+
+    payload = {
+        "iss": django_settings.USER_ACCESS_TOKEN_ISSUER,
+        "aud": django_settings.USER_ACCESS_TOKEN_AUDIENCE,
+        "iat": now,
+        "exp": now + timedelta(seconds=django_settings.USER_ACCESS_TOKEN_TTL),
+        "user_id": str(user.id),
+        "token_type": "user_access",
+        "client_id": "test-app",
+        "scope": "user:access",
+    }
+
+    return jwt.encode(
+        payload,
+        django_settings.USER_ACCESS_TOKEN_SECRET_KEY,
+        algorithm=django_settings.USER_ACCESS_TOKEN_ALG,
+    )
+
+
+def test_api_rooms_create_authenticated_with_user_access_token():
+    """A user access token should create a room exactly like a session would."""
+    user = UserFactory()
+
+    client = APIClient()
+    client.credentials(HTTP_AUTHORIZATION=f"Bearer {generate_user_access_token(user)}")
+    response = client.post("/api/v1.0/rooms/", {"name": "my room"})
+
+    assert response.status_code == 201
+    room = Room.objects.get()
+    assert room.accesses.filter(role="owner", user=user).exists()

src/backend/core/tests/rooms/test_api_rooms_list.py

@@ -2,8 +2,12 @@
 Test rooms API endpoints in the Meet core app: list.
 """
 
+from datetime import datetime, timedelta, timezone
 from unittest import mock
 
+from django.conf import settings as django_settings
+
+import jwt
 import pytest
 from rest_framework.pagination import PageNumberPagination
 from rest_framework.test import APIClient
@@ -156,3 +160,40 @@ def test_api_rooms_list_pagination_page_size():
     assert len(content["results"]) == 3
     assert content["next"] == "http://testserver/api/v1.0/rooms/?page=2&page_size=3"
     assert content["previous"] is None
+
+
+def generate_user_access_token(user):
+    """Generate a valid user access JWT signed with the token secret."""
+    now = datetime.now(timezone.utc)
+
+    payload = {
+        "iss": django_settings.USER_ACCESS_TOKEN_ISSUER,
+        "aud": django_settings.USER_ACCESS_TOKEN_AUDIENCE,
+        "iat": now,
+        "exp": now + timedelta(seconds=django_settings.USER_ACCESS_TOKEN_TTL),
+        "user_id": str(user.id),
+        "token_type": "user_access",
+        "client_id": "test-app",
+        "scope": "user:access",
+    }
+
+    return jwt.encode(
+        payload,
+        django_settings.USER_ACCESS_TOKEN_SECRET_KEY,
+        algorithm=django_settings.USER_ACCESS_TOKEN_ALG,
+    )
+
+
+def test_api_rooms_list_authenticated_with_user_access_token():
+    """A user access token should list rooms exactly like a session would."""
+    user = UserFactory()
+    room = RoomFactory(users=[(user, "owner")])
+    RoomFactory()  # another user's room, not listed
+
+    client = APIClient()
+    client.credentials(HTTP_AUTHORIZATION=f"Bearer {generate_user_access_token(user)}")
+    response = client.get("/api/v1.0/rooms/")
+
+    assert response.status_code == 200
+    assert response.data["count"] == 1
+    assert response.data["results"][0]["id"] == str(room.id)

src/backend/core/tests/rooms/test_api_rooms_retrieve.py

@@ -3,11 +3,14 @@ Test rooms API endpoints in the Meet core app: retrieve.
 """
 
 import random
+from datetime import datetime, timedelta, timezone
 from unittest import mock
 
+from django.conf import settings as django_settings
 from django.contrib.auth.models import AnonymousUser
 from django.test.utils import override_settings
 
+import jwt
 import pytest
 from rest_framework.test import APIClient
 
@@ -503,3 +506,40 @@ def test_api_rooms_retrieve_administrators(
         role=str(user_access.role),
         participant_id=None,
     )
+
+
+def generate_user_access_token(user):
+    """Generate a valid user access JWT signed with the token secret."""
+    now = datetime.now(timezone.utc)
+
+    payload = {
+        "iss": django_settings.USER_ACCESS_TOKEN_ISSUER,
+        "aud": django_settings.USER_ACCESS_TOKEN_AUDIENCE,
+        "iat": now,
+        "exp": now + timedelta(seconds=django_settings.USER_ACCESS_TOKEN_TTL),
+        "user_id": str(user.id),
+        "token_type": "user_access",
+        "client_id": "test-app",
+        "scope": "user:access",
+    }
+
+    return jwt.encode(
+        payload,
+        django_settings.USER_ACCESS_TOKEN_SECRET_KEY,
+        algorithm=django_settings.USER_ACCESS_TOKEN_ALG,
+    )
+
+
+def test_api_rooms_retrieve_authenticated_with_user_access_token():
+    """A user access token should retrieve a room exactly like a session would."""
+    user = UserFactory()
+    room = RoomFactory(users=[(user, "owner")])
+
+    client = APIClient()
+    client.credentials(HTTP_AUTHORIZATION=f"Bearer {generate_user_access_token(user)}")
+    response = client.get(f"/api/v1.0/rooms/{room.id!s}/")
+
+    assert response.status_code == 200
+    assert response.data["id"] == str(room.id)
+    # Authenticated as the owner: privileged fields are included
+    assert response.data["pin_code"] == room.pin_code

src/backend/core/tests/rooms/test_api_rooms_update.py

@@ -3,8 +3,12 @@ Test rooms API endpoints in the Meet core app: update.
 """
 
 import random
+from datetime import datetime, timedelta, timezone
 from unittest.mock import patch
 
+from django.conf import settings as django_settings
+
+import jwt
 import pytest
 from rest_framework.test import APIClient
 
@@ -437,3 +441,45 @@ def test_api_rooms_update_livekit_sync_failure(mock_update_metadata):
             "configuration": {"can_publish_sources": ["camera"]},
         },
     )
+
+
+def generate_user_access_token(user):
+    """Generate a valid user access JWT signed with the token secret."""
+    now = datetime.now(timezone.utc)
+
+    payload = {
+        "iss": django_settings.USER_ACCESS_TOKEN_ISSUER,
+        "aud": django_settings.USER_ACCESS_TOKEN_AUDIENCE,
+        "iat": now,
+        "exp": now + timedelta(seconds=django_settings.USER_ACCESS_TOKEN_TTL),
+        "user_id": str(user.id),
+        "token_type": "user_access",
+        "client_id": "test-app",
+        "scope": "user:access",
+    }
+
+    return jwt.encode(
+        payload,
+        django_settings.USER_ACCESS_TOKEN_SECRET_KEY,
+        algorithm=django_settings.USER_ACCESS_TOKEN_ALG,
+    )
+
+
+def test_api_rooms_update_authenticated_with_user_access_token():
+    """Role-based permissions apply unchanged with a user access token."""
+    user = UserFactory()
+    room = RoomFactory(users=[(user, "member")])
+
+    client = APIClient()
+    client.credentials(HTTP_AUTHORIZATION=f"Bearer {generate_user_access_token(user)}")
+
+    # A simple member cannot update the room
+    response = client.patch(f"/api/v1.0/rooms/{room.id!s}/", {"name": "new name"})
+    assert response.status_code == 403
+
+    # An administrator can
+    room.accesses.filter(user=user).update(role="administrator")
+    response = client.patch(f"/api/v1.0/rooms/{room.id!s}/", {"name": "new name"})
+    assert response.status_code == 200
+    room.refresh_from_db()
+    assert room.name == "new name"

src/backend/core/tests/services/test_transit_code.py

@@ -0,0 +1,46 @@
+"""
+Unit tests for the TransitCodeService.
+"""
+
+import pytest
+
+from core.factories import UserFactory
+from core.services.transit_code import TransitCodeService
+
+pytestmark = pytest.mark.django_db
+
+
+def test_create_code_returns_unique_opaque_codes():
+    """Each created code should be a distinct high-entropy string."""
+    user = UserFactory()
+    service = TransitCodeService()
+
+    codes = {service.create_code(user) for _ in range(5)}
+
+    assert len(codes) == 5
+    for code in codes:
+        assert len(code) >= 43
+
+
+def test_consume_code_returns_stored_data_once():
+    """Consuming a code should return its data exactly once."""
+    user = UserFactory()
+    service = TransitCodeService()
+
+    code = service.create_code(user, client_id="my-app")
+
+    assert service.consume_code(code) == {
+        "user_id": str(user.id),
+        "client_id": "my-app",
+    }
+    # Single use: a second consumption fails
+    assert service.consume_code(code) is None
+
+
+def test_consume_code_unknown_or_empty():
+    """Unknown or empty codes should not be consumable."""
+    service = TransitCodeService()
+
+    assert service.consume_code("unknown-code") is None
+    assert service.consume_code("") is None
+    assert service.consume_code(None) is None

src/backend/core/tests/test_api_user_access_token_authentication.py

@@ -0,0 +1,200 @@
+"""
+Tests for user access JWT authentication on the core API.
+
+The token authenticates the user on the whole API, exactly like a session
+cookie would (similar to lib-jitsi-meet's token authentication): the
+existing role-based permissions apply unchanged. Room endpoint coverage
+with a user access token lives in the room test files.
+"""
+
+from datetime import datetime, timedelta, timezone
+
+from django.conf import settings as django_settings
+
+import jwt
+import pytest
+from rest_framework.test import APIClient
+
+from core.factories import RoomFactory, UserFactory
+from core.models import RoleChoices
+
+pytestmark = pytest.mark.django_db
+
+
+def generate_user_access_token(user, **overrides):
+    """Generate a valid user access JWT signed with the token secret."""
+    now = datetime.now(timezone.utc)
+
+    payload = {
+        "iss": django_settings.USER_ACCESS_TOKEN_ISSUER,
+        "aud": django_settings.USER_ACCESS_TOKEN_AUDIENCE,
+        "iat": now,
+        "exp": now + timedelta(seconds=django_settings.USER_ACCESS_TOKEN_TTL),
+        "user_id": str(user.id),
+        "token_type": "user_access",
+        "client_id": "test-app",
+        "scope": "user:access",
+    }
+    payload.update(overrides)
+    payload = {key: value for key, value in payload.items() if value is not None}
+
+    return jwt.encode(
+        payload,
+        django_settings.USER_ACCESS_TOKEN_SECRET_KEY,
+        algorithm=django_settings.USER_ACCESS_TOKEN_ALG,
+    )
+
+
+def test_user_access_token_users_me():
+    """A user access token should authenticate the user on /users/me/."""
+    user = UserFactory()
+
+    client = APIClient()
+    client.credentials(HTTP_AUTHORIZATION=f"Bearer {generate_user_access_token(user)}")
+
+    response = client.get("/api/v1.0/users/me/")
+
+    assert response.status_code == 200
+    assert response.data["email"] == user.email
+
+
+def test_user_access_token_expired():
+    """An expired user access token should be rejected."""
+    user = UserFactory()
+
+    now = datetime.now(timezone.utc)
+    token = generate_user_access_token(
+        user,
+        iat=now - timedelta(hours=3),
+        exp=now - timedelta(hours=1),
+    )
+    client = APIClient()
+    client.credentials(HTTP_AUTHORIZATION=f"Bearer {token}")
+
+    response = client.get("/api/v1.0/users/me/")
+
+    assert response.status_code == 401
+    assert "token expired" in str(response.data).lower()
+
+
+def test_user_access_token_invalid_signature():
+    """A token signed with the wrong key should defer and end unauthenticated."""
+    user = UserFactory()
+
+    now = datetime.now(timezone.utc)
+    token = jwt.encode(
+        {
+            "iss": django_settings.USER_ACCESS_TOKEN_ISSUER,
+            "aud": django_settings.USER_ACCESS_TOKEN_AUDIENCE,
+            "iat": now,
+            "exp": now + timedelta(seconds=600),
+            "user_id": str(user.id),
+            "token_type": "user_access",
+            "client_id": "test-app",
+        },
+        "wrong-secret-key-padded-for-minimum-len!",
+        algorithm=django_settings.USER_ACCESS_TOKEN_ALG,
+    )
+    client = APIClient()
+    client.credentials(HTTP_AUTHORIZATION=f"Bearer {token}")
+
+    # UserAccessJWTAuthentication defers, session auth finds no session
+    response = client.get("/api/v1.0/users/me/")
+
+    assert response.status_code == 401
+
+
+def test_user_access_token_wrong_token_type():
+    """A verified token with the wrong 'token_type' claim should be rejected."""
+    user = UserFactory()
+
+    token = generate_user_access_token(user, token_type="addons")
+    client = APIClient()
+    client.credentials(HTTP_AUTHORIZATION=f"Bearer {token}")
+
+    response = client.get("/api/v1.0/users/me/")
+
+    assert response.status_code == 401
+    assert "invalid token type" in str(response.data).lower()
+
+
+def test_user_access_token_missing_client_id_claim():
+    """A token without the issuance-audit claim should be rejected."""
+    user = UserFactory()
+
+    token = generate_user_access_token(user, client_id=None)
+    client = APIClient()
+    client.credentials(HTTP_AUTHORIZATION=f"Bearer {token}")
+
+    response = client.get("/api/v1.0/users/me/")
+
+    assert response.status_code == 401
+    assert "invalid token claims" in str(response.data).lower()
+
+
+def test_user_access_token_inactive_user():
+    """A user access token for an inactive user should be rejected."""
+    user = UserFactory(is_active=False)
+
+    client = APIClient()
+    client.credentials(HTTP_AUTHORIZATION=f"Bearer {generate_user_access_token(user)}")
+
+    response = client.get("/api/v1.0/users/me/")
+
+    assert response.status_code == 401
+
+
+def test_user_access_token_feature_disabled(settings):
+    """When the feature is disabled, user access tokens should be ignored."""
+    settings.USER_ACCESS_TOKEN_ENABLED = False
+
+    user = UserFactory()
+
+    client = APIClient()
+    client.credentials(HTTP_AUTHORIZATION=f"Bearer {generate_user_access_token(user)}")
+
+    response = client.get("/api/v1.0/users/me/")
+
+    assert response.status_code == 401
+
+
+def test_user_access_token_does_not_break_session_authentication():
+    """A session-authenticated user should keep full access to the API."""
+    user = UserFactory()
+    RoomFactory(users=[(user, RoleChoices.OWNER)])
+
+    client = APIClient()
+    client.force_login(user)
+    response = client.get("/api/v1.0/rooms/")
+
+    assert response.status_code == 200
+    assert response.data["count"] == 1
+
+
+def test_user_access_token_application_jwt_not_accepted_on_core_api():
+    """An application-delegation JWT must not authenticate on the core API."""
+    user = UserFactory()
+
+    now = datetime.now(timezone.utc)
+    token = jwt.encode(
+        {
+            "iss": django_settings.APPLICATION_JWT_ISSUER,
+            "aud": django_settings.APPLICATION_JWT_AUDIENCE,
+            "iat": now,
+            "exp": now + timedelta(seconds=600),
+            "user_id": str(user.id),
+            "client_id": "some-client",
+            "delegated": True,
+            "scope": "rooms:retrieve",
+        },
+        django_settings.APPLICATION_JWT_SECRET_KEY,
+        algorithm=django_settings.APPLICATION_JWT_ALG,
+    )
+    client = APIClient()
+    client.credentials(HTTP_AUTHORIZATION=f"Bearer {token}")
+
+    # The user token backend must defer (wrong signature) and the request
+    # must end up unauthenticated.
+    response = client.get("/api/v1.0/users/me/")
+
+    assert response.status_code == 401

src/backend/core/tests/test_api_users_exchange_access_token.py

@@ -0,0 +1,165 @@
+"""
+Test users API endpoints in the Meet core app: exchange transit code.
+"""
+
+# pylint: disable=W0621
+
+import secrets
+
+import jwt
+import pytest
+from rest_framework.test import APIClient
+
+from core.factories import UserFactory
+from core.services.transit_code import TransitCodeService
+
+pytestmark = pytest.mark.django_db
+
+
+def decode_user_access_token(token, settings):
+    """Decode a user access token with the token secret."""
+    return jwt.decode(
+        token,
+        settings.USER_ACCESS_TOKEN_SECRET_KEY,
+        algorithms=[settings.USER_ACCESS_TOKEN_ALG],
+        issuer=settings.USER_ACCESS_TOKEN_ISSUER,
+        audience=settings.USER_ACCESS_TOKEN_AUDIENCE,
+    )
+
+
+def generate_unknown_code(settings):
+    """Generate a well-formed code that was never stored."""
+    return secrets.token_urlsafe(settings.TRANSIT_CODE_NBYTES)
+
+
+@pytest.fixture
+def client():
+    """Return an anonymous API client with a random source IP.
+
+    A fresh IP per test isolates the anonymous throttle history, both
+    between the tests of this module and between test runs.
+    """
+    # `secrets` rather than `random`: the global random module is seeded
+    # deterministically by the factories, its sequence repeats across runs.
+    remote_addr = (
+        f"10.{secrets.randbelow(256)}.{secrets.randbelow(256)}"
+        f".{secrets.randbelow(254) + 1}"
+    )
+    return APIClient(REMOTE_ADDR=remote_addr)
+
+
+def test_exchange_access_token_missing_code(client):
+    """The exchange endpoint should validate its input."""
+    response = client.post("/api/v1.0/users/exchange-access-token/")
+
+    assert response.status_code == 400
+    assert "code" in response.data
+
+
+def test_exchange_access_token_malformed_code(client):
+    """A code whose length cannot match a generated one should be a 400."""
+    response = client.post(
+        "/api/v1.0/users/exchange-access-token/",
+        {"code": "not-a-valid-code"},
+    )
+
+    assert response.status_code == 400
+    assert "invalid transit code format" in str(response.data).lower()
+
+
+def test_exchange_access_token_unknown_code(client, settings):
+    """A well-formed but unknown code should be denied."""
+    response = client.post(
+        "/api/v1.0/users/exchange-access-token/",
+        {"code": generate_unknown_code(settings)},
+    )
+
+    assert response.status_code == 403
+    assert "invalid, expired or already used" in str(response.data).lower()
+
+
+def test_exchange_access_token_success(client, settings):
+    """A valid transit code should be exchangeable for an access token."""
+    user = UserFactory()
+
+    code = TransitCodeService().create_code(user, client_id="my-app")
+
+    response = client.post("/api/v1.0/users/exchange-access-token/", {"code": code})
+
+    assert response.status_code == 200
+    assert response.data["token_type"] == settings.USER_ACCESS_TOKEN_TYPE
+    assert response.data["expires_in"] == settings.USER_ACCESS_TOKEN_TTL
+    assert response.data["scope"] == "user:access"
+
+    payload = decode_user_access_token(response.data["access_token"], settings)
+    assert payload["token_type"] == "user_access"
+    assert payload["user_id"] == str(user.id)
+    assert payload["client_id"] == "my-app"
+    assert payload["exp"] - payload["iat"] == settings.USER_ACCESS_TOKEN_TTL
+
+
+def test_exchange_access_token_single_use(client):
+    """A transit code should be exchangeable exactly once."""
+    user = UserFactory()
+
+    code = TransitCodeService().create_code(user)
+
+    response = client.post("/api/v1.0/users/exchange-access-token/", {"code": code})
+    assert response.status_code == 200
+
+    # Replaying the same code must be denied
+    response = client.post("/api/v1.0/users/exchange-access-token/", {"code": code})
+    assert response.status_code == 403
+    assert "invalid, expired or already used" in str(response.data).lower()
+
+
+def test_exchange_access_token_inactive_user(client):
+    """A code minted for a now-inactive user should be denied."""
+    user = UserFactory()
+
+    code = TransitCodeService().create_code(user)
+
+    user.is_active = False
+    user.save()
+
+    response = client.post("/api/v1.0/users/exchange-access-token/", {"code": code})
+
+    assert response.status_code == 403
+    assert "no longer access" in str(response.data).lower()
+
+
+def test_exchange_access_token_feature_disabled(client, settings):
+    """The exchange endpoint should return 404 when the feature is disabled."""
+    settings.USER_ACCESS_TOKEN_ENABLED = False
+
+    user = UserFactory()
+    code = TransitCodeService().create_code(user)
+
+    response = client.post("/api/v1.0/users/exchange-access-token/", {"code": code})
+
+    assert response.status_code == 404
+
+
+def test_exchange_access_token_throttled(client, settings):
+    """Anonymous exchange attempts should be rate limited."""
+    throttle_rates = settings.REST_FRAMEWORK["DEFAULT_THROTTLE_RATES"]
+    initial_rate = throttle_rates["exchange_access_token"]
+    # The rates dict is mutated in place: restore it explicitly, the
+    # `settings` fixture only rolls back attribute assignments.
+    throttle_rates["exchange_access_token"] = "2/minute"
+
+    try:
+        for _ in range(2):
+            response = client.post(
+                "/api/v1.0/users/exchange-access-token/",
+                {"code": generate_unknown_code(settings)},
+            )
+            assert response.status_code == 403
+
+        response = client.post(
+            "/api/v1.0/users/exchange-access-token/",
+            {"code": generate_unknown_code(settings)},
+        )
+        assert response.status_code == 429
+    finally:
+        throttle_rates["exchange_access_token"] = initial_rate

src/backend/core/tests/test_external_api_users.py

@@ -0,0 +1,166 @@
+"""
+Tests for external API /users endpoints (transit codes)
+"""
+
+# pylint: disable=W0621
+
+from datetime import datetime, timedelta, timezone
+from unittest import mock
+
+from django.conf import settings as django_settings
+
+import jwt
+import pytest
+from lasuite.oidc_resource_server.authentication import ResourceServerAuthentication
+from rest_framework.test import APIClient
+
+from core.factories import ApplicationFactory, UserFactory
+from core.models import ApplicationScope
+from core.services.transit_code import TransitCodeService
+
+pytestmark = pytest.mark.django_db
+
+
+def generate_test_token(user, scopes):
+    """Generate a valid application JWT token for testing."""
+    now = datetime.now(timezone.utc)
+    scope_string = " ".join(scopes)
+
+    application = ApplicationFactory()
+
+    payload = {
+        "iss": django_settings.APPLICATION_JWT_ISSUER,
+        "aud": django_settings.APPLICATION_JWT_AUDIENCE,
+        "iat": now,
+        "exp": now
+        + timedelta(seconds=django_settings.APPLICATION_JWT_EXPIRATION_SECONDS),
+        "client_id": str(application.client_id),
+        "scope": scope_string,
+        "user_id": str(user.id),
+        "delegated": True,
+    }
+
+    return jwt.encode(
+        payload,
+        django_settings.APPLICATION_JWT_SECRET_KEY,
+        algorithm=django_settings.APPLICATION_JWT_ALG,
+    )
+
+
+def test_api_users_transit_code_requires_authentication():
+    """Minting a transit code without authentication should return 401."""
+    client = APIClient()
+    response = client.post("/external-api/v1.0/users/transit-code/")
+
+    assert response.status_code == 401
+
+
+def test_api_users_transit_code_missing_scope():
+    """A token without the 'users:session' scope should be rejected."""
+    user = UserFactory()
+
+    token = generate_test_token(user, [ApplicationScope.ROOMS_RETRIEVE])
+
+    client = APIClient()
+    client.credentials(HTTP_AUTHORIZATION=f"Bearer {token}")
+    response = client.post("/external-api/v1.0/users/transit-code/")
+
+    assert response.status_code == 403
+    assert "users:session" in str(response.data)
+
+
+def test_api_users_transit_code_success(settings):
+    """A delegated user with the scope should be able to mint a transit code."""
+    user = UserFactory()
+
+    token = generate_test_token(user, [ApplicationScope.USERS_SESSION])
+
+    client = APIClient()
+    client.credentials(HTTP_AUTHORIZATION=f"Bearer {token}")
+    response = client.post("/external-api/v1.0/users/transit-code/")
+
+    assert response.status_code == 200
+    assert response.data["expires_in"] == settings.TRANSIT_CODE_TTL
+
+    code = response.data["transit_code"]
+    # Opaque, high-entropy random string
+    assert len(code) == (4 * settings.TRANSIT_CODE_NBYTES + 2) // 3
+
+    # The code is stored server-side and references the delegated user
+    code_data = TransitCodeService().consume_code(code)
+    assert code_data == {
+        "user_id": str(user.id),
+        "client_id": mock.ANY,
+    }
+
+
+def test_api_users_transit_code_with_rs_token():
+    """A resource-server-authenticated user should be able to mint a code."""
+    user = UserFactory()
+
+    # todo - add a decorator instead
+    with mock.patch.object(
+        ResourceServerAuthentication,
+        "authenticate",
+        return_value=(user, {"scope": "users:session", "client_id": "rs-client"}),
+    ) as mock_rs_authenticate:
+        client = APIClient()
+        client.credentials(HTTP_AUTHORIZATION="Bearer some-opaque-rs-token")
+        response = client.post("/external-api/v1.0/users/transit-code/")
+
+    mock_rs_authenticate.assert_called_once()
+    assert response.status_code == 200
+
+    code_data = TransitCodeService().consume_code(response.data["transit_code"])
+    assert code_data == {
+        "user_id": str(user.id),
+        "client_id": "rs-client",
+    }
+
+
+def test_api_users_transit_code_with_rs_token_missing_scope():
+    """A resource server token without the scope should be rejected."""
+    user = UserFactory()
+
+    # todo - add a decorator instead
+    with mock.patch.object(
+        ResourceServerAuthentication,
+        "authenticate",
+        return_value=(user, {"scope": "rooms:list", "client_id": "rs-client"}),
+    ):
+        client = APIClient()
+        client.credentials(HTTP_AUTHORIZATION="Bearer some-opaque-rs-token")
+        response = client.post("/external-api/v1.0/users/transit-code/")
+
+    assert response.status_code == 403
+    assert "users:session" in str(response.data)
+
+
+def test_api_users_transit_code_feature_disabled(settings):
+    """Minting a transit code should return 404 when the feature is disabled."""
+    settings.USER_ACCESS_TOKEN_ENABLED = False
+
+    user = UserFactory()
+    token = generate_test_token(user, [ApplicationScope.USERS_SESSION])
+
+    client = APIClient()
+    client.credentials(HTTP_AUTHORIZATION=f"Bearer {token}")
+    response = client.post("/external-api/v1.0/users/transit-code/")
+
+    assert response.status_code == 404
+
+
+def test_api_users_transit_code_inactive_user():
+    """An inactive user should not be able to mint a transit code."""
+    user = UserFactory(is_active=False)
+
+    token = generate_test_token(user, [ApplicationScope.USERS_SESSION])
+
+    client = APIClient()
+    client.credentials(HTTP_AUTHORIZATION=f"Bearer {token}")
+    response = client.post("/external-api/v1.0/users/transit-code/")
+
+    assert response.status_code == 401
+
+
+# todo - add a test to make sure the addon authentification doesn't allow to mint a transit token

src/backend/core/urls.py

@@ -37,6 +37,11 @@ external_router.register(
     external_viewsets.RoomViewSet,
     basename="external_room",
 )
+external_router.register(
+    "users",
+    external_viewsets.UserViewSet,
+    basename="external_user",
+)
 
 urlpatterns = [
     path(

src/backend/meet/settings.py

@@ -324,6 +324,7 @@ class Base(Configuration):
 
     REST_FRAMEWORK = {
         "DEFAULT_AUTHENTICATION_CLASSES": (
+            "core.authentication.user_token.UserAccessJWTAuthentication",
             "core.authentication.backends.SessionAuthenticationWith401",
         ),
         "DEFAULT_PARSER_CLASSES": [
@@ -344,6 +345,11 @@ class Base(Configuration):
                 environ_name="REQUEST_ENTRY_THROTTLE_RATES",
                 environ_prefix=None,
             ),
+            "exchange_access_token": values.Value(
+                default="30/minute",
+                environ_name="EXCHANGE_ACCESS_TOKEN_THROTTLE_RATES",
+                environ_prefix=None,
+            ),
             "creation_callback": values.Value(
                 default="600/minute",
                 environ_name="CREATION_CALLBACK_THROTTLE_RATES",
@@ -953,6 +959,61 @@ class Base(Configuration):
         environ_name="APPLICATION_BASE_URL",
         environ_prefix=None,
     )
+
+    # User access tokens (embedded frontend / iframe support)
+    USER_ACCESS_TOKEN_ENABLED = values.BooleanValue(
+        False, environ_name="USER_ACCESS_TOKEN_ENABLED", environ_prefix=None
+    )
+    USER_ACCESS_TOKEN_SECRET_KEY = SecretFileValue(
+        None, environ_name="USER_ACCESS_TOKEN_SECRET_KEY", environ_prefix=None
+    )
+    USER_ACCESS_TOKEN_ALG = values.Value(
+        "HS256",
+        environ_name="USER_ACCESS_TOKEN_ALG",
+        environ_prefix=None,
+    )
+    USER_ACCESS_TOKEN_ISSUER = values.Value(
+        "lasuite-meet",
+        environ_name="USER_ACCESS_TOKEN_ISSUER",
+        environ_prefix=None,
+    )
+    USER_ACCESS_TOKEN_AUDIENCE = values.Value(
+        None,
+        environ_name="USER_ACCESS_TOKEN_AUDIENCE",
+        environ_prefix=None,
+    )
+    # Lifetime of the user access token obtained through the exchange
+    # endpoint. It never transits through a URL, so it can cover a full
+    # meeting (default: 2 hours).
+    USER_ACCESS_TOKEN_TTL = values.PositiveIntegerValue(
+        7200,
+        environ_name="USER_ACCESS_TOKEN_TTL",
+        environ_prefix=None,
+    )
+    # Lifetime of the single-use transit code handed to the frontend
+    # through a URL fragment. Kept very short by design: it must only
+    # survive the redirect and the exchange call.
+    TRANSIT_CODE_TTL = values.PositiveIntegerValue(
+        60,
+        environ_name="TRANSIT_CODE_TTL",
+        environ_prefix=None,
+    )
+    TRANSIT_CODE_CACHE_PREFIX = values.Value(
+        "transit-code",
+        environ_name="TRANSIT_CODE_CACHE_PREFIX",
+        environ_prefix=None,
+    )
+    # Number of random bytes per code (48 bytes -> 64 url-safe characters)
+    TRANSIT_CODE_NBYTES = values.PositiveIntegerValue(
+        48,
+        environ_name="TRANSIT_CODE_NBYTES",
+        environ_prefix=None,
+    )
+    USER_ACCESS_TOKEN_TYPE = values.Value(
+        "Bearer",
+        environ_name="USER_ACCESS_TOKEN_TYPE",
+        environ_prefix=None,
+    )
     # Warning: EXTERNAL_API_ALLOW_PUBLIC_ACCESS is ignored when
     # EXTERNAL_API_DEFAULT_ACCESS_LEVEL=public.
     EXTERNAL_API_ALLOW_PUBLIC_ACCESS = values.BooleanValue(
@@ -1250,6 +1311,10 @@ class Test(Base):
     ADDONS_CSRF_SECRET = "secret-key-padded-for-minimum-len!-addons"  # noqa:S105
     ADDONS_TOKEN_SECRET_KEY = "secret-key-padded-for-minimum-len!-addons"  # noqa:S105
 
+    USER_ACCESS_TOKEN_ENABLED = True
+    USER_ACCESS_TOKEN_SECRET_KEY = "secret-key-padded-for-minimum-len!-room"  # noqa:S105
+    USER_ACCESS_TOKEN_AUDIENCE = "Test inc."  # noqa:S105
+
     def __init__(self):
         # pylint: disable=invalid-name
         self.INSTALLED_APPS += ["drf_spectacular_sidecar"]