feat: implement dynamic client registration (#7096)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: Zaimwa9

api/app/settings/common.py

@@ -303,6 +303,7 @@
 
 
 LOGIN_THROTTLE_RATE = env("LOGIN_THROTTLE_RATE", "20/min")
+DCR_THROTTLE_RATE = env("DCR_THROTTLE_RATE", "500/month")
 SIGNUP_THROTTLE_RATE = env("SIGNUP_THROTTLE_RATE", "10000/min")
 USER_THROTTLE_RATE = env("USER_THROTTLE_RATE", default=None)
 MASTER_API_KEY_THROTTLE_RATE = env("MASTER_API_KEY_THROTTLE_RATE", default=None)
@@ -321,6 +322,7 @@
     "DEFAULT_THROTTLE_CLASSES": DEFAULT_THROTTLE_CLASSES,
     "DEFAULT_THROTTLE_RATES": {
         "login": LOGIN_THROTTLE_RATE,
+        "dcr_register": DCR_THROTTLE_RATE,
         "signup": SIGNUP_THROTTLE_RATE,
         "master_api_key": MASTER_API_KEY_THROTTLE_RATE,
         "mfa_code": "5/min",

api/app/settings/test.py

@@ -7,6 +7,7 @@
 REST_FRAMEWORK["DEFAULT_THROTTLE_CLASSES"] = ["core.throttling.UserRateThrottle"]
 REST_FRAMEWORK["DEFAULT_THROTTLE_RATES"] = {
     "login": "100/min",
+    "dcr_register": "100/min",
     "mfa_code": "5/min",
     "invite": "10/min",
     "signup": "100/min",

api/app/urls.py

@@ -7,7 +7,10 @@
 from django.views.generic.base import TemplateView
 from oauth2_provider import views as oauth2_views
 
-from oauth2_metadata.views import authorization_server_metadata
+from oauth2_metadata.views import (
+    DynamicClientRegistrationView,
+    authorization_server_metadata,
+)
 from users.views import password_reset_redirect
 
 from . import views
@@ -54,6 +57,11 @@
             "robots.txt",
             TemplateView.as_view(template_name="robots.txt", content_type="text/plain"),
         ),
+        path(
+            "o/register/",
+            DynamicClientRegistrationView.as_view(),
+            name="oauth2-dcr-register",
+        ),
         path(
             "o/",
             include(

api/oauth2_metadata/serializers.py

@@ -0,0 +1,79 @@
+import re
+
+from django.core.exceptions import ValidationError as DjangoValidationError
+from rest_framework import serializers
+
+from oauth2_metadata.services import validate_redirect_uri
+
+# Allow ASCII letters, digits, spaces, hyphens, underscores, dots, and parentheses.
+# ASCII-only to prevent Unicode homoglyph spoofing on the consent screen.
+_CLIENT_NAME_RE = re.compile(r"^[\w\s.\-()]+$", re.ASCII)
+
+
+class DCRRequestSerializer(serializers.Serializer[None]):
+    client_name = serializers.CharField(max_length=255, required=True)
+    redirect_uris = serializers.ListField(
+        child=serializers.URLField(),
+        min_length=1,
+        max_length=5,
+        required=True,
+    )
+    grant_types = serializers.ListField(
+        child=serializers.CharField(),
+        required=False,
+        default=["authorization_code", "refresh_token"],
+    )
+    response_types = serializers.ListField(
+        child=serializers.CharField(),
+        required=False,
+        default=["code"],
+    )
+    token_endpoint_auth_method = serializers.CharField(
+        required=False,
+        default="none",
+    )
+
+    def validate_client_name(self, value: str) -> str:
+        if not _CLIENT_NAME_RE.match(value):
+            raise serializers.ValidationError(
+                "Client name may only contain letters, digits, spaces, "
+                "hyphens, underscores, dots, and parentheses."
+            )
+        return value
+
+    def validate_redirect_uris(self, value: list[str]) -> list[str]:
+        errors: list[str] = []
+        for uri in value:
+            try:
+                validate_redirect_uri(uri)
+            except DjangoValidationError as e:
+                errors.append(str(e.message))
+        if errors:
+            raise serializers.ValidationError(errors)
+        return value
+
+    def validate_token_endpoint_auth_method(self, value: str) -> str:
+        if value != "none":
+            raise serializers.ValidationError(
+                "Only public clients are supported; "
+                "token_endpoint_auth_method must be 'none'."
+            )
+        return value
+
+    def validate_grant_types(self, value: list[str]) -> list[str]:
+        allowed = {"authorization_code", "refresh_token"}
+        invalid = set(value) - allowed
+        if invalid:
+            raise serializers.ValidationError(
+                f"Unsupported grant types: {', '.join(sorted(invalid))}"
+            )
+        return value
+
+    def validate_response_types(self, value: list[str]) -> list[str]:
+        allowed = {"code"}
+        invalid = set(value) - allowed
+        if invalid:
+            raise serializers.ValidationError(
+                f"Unsupported response types: {', '.join(sorted(invalid))}"
+            )
+        return value

api/oauth2_metadata/services.py

@@ -0,0 +1,59 @@
+import logging
+from urllib.parse import urlparse
+
+from django.core.exceptions import ValidationError
+from oauth2_provider.models import Application
+
+logger = logging.getLogger(__name__)
+
+
+def validate_redirect_uri(uri: str) -> str:
+    """Validate a single redirect URI per DCR policy.
+
+    Rules:
+    - HTTPS required for all redirect URIs
+    - No wildcards, exact match only
+    - No fragment components
+    - localhost exception: http://localhost:*, http://127.0.0.1:*, and http://[::1]:* permitted
+    """
+    parsed = urlparse(uri)
+
+    if not parsed.scheme or not parsed.netloc:
+        raise ValidationError(f"Invalid URI: {uri}")
+
+    if "*" in uri:
+        raise ValidationError(f"Wildcards are not permitted in redirect URIs: {uri}")
+
+    if parsed.fragment:
+        raise ValidationError(f"Fragment components are not permitted: {uri}")
+
+    is_localhost = parsed.hostname in ("localhost", "127.0.0.1", "::1")
+
+    if parsed.scheme != "https" and not (parsed.scheme == "http" and is_localhost):
+        raise ValidationError(
+            f"HTTPS is required for redirect URIs (localhost excepted): {uri}"
+        )
+
+    return uri
+
+
+def create_oauth2_application(
+    *,
+    client_name: str,
+    redirect_uris: list[str],
+) -> Application:
+    """Create a public OAuth2 application for dynamic client registration."""
+    application: Application = Application.objects.create(
+        name=client_name,
+        client_type=Application.CLIENT_PUBLIC,
+        authorization_grant_type=Application.GRANT_AUTHORIZATION_CODE,
+        client_secret="",
+        redirect_uris=" ".join(redirect_uris),
+        skip_authorization=False,
+    )
+    logger.info(
+        "OAuth2 DCR: registered application %s (client_id=%s).",
+        client_name,
+        application.client_id,
+    )
+    return application

api/oauth2_metadata/tasks.py

@@ -1,9 +1,37 @@
+import logging
 from datetime import timedelta
 
 from django.core.management import call_command
+from django.utils import timezone
 from task_processor.decorators import register_recurring_task
 
+logger = logging.getLogger(__name__)
+
 
 @register_recurring_task(run_every=timedelta(hours=24))
 def clear_expired_oauth2_tokens() -> None:
     call_command("cleartokens")
+
+
+@register_recurring_task(run_every=timedelta(hours=24))
+def cleanup_stale_oauth2_applications() -> None:
+    """Remove DCR applications that were never used to obtain a token.
+
+    An application is considered stale if it was registered more than 14 days
+    ago and has no associated access tokens, refresh tokens, or grants.
+    """
+    from django.db.models import Exists, OuterRef
+    from oauth2_provider.models import AccessToken, Application, Grant, RefreshToken
+
+    threshold = timezone.now() - timedelta(days=14)
+    stale = Application.objects.filter(
+        created__lt=threshold,
+        user__isnull=True,  # Only DCR-created apps (no user)
+    ).exclude(
+        Exists(AccessToken.objects.filter(application=OuterRef("pk")))
+        | Exists(RefreshToken.objects.filter(application=OuterRef("pk")))
+        | Exists(Grant.objects.filter(application=OuterRef("pk")))
+    )
+    count, _ = stale.delete()
+    if count:
+        logger.info("OAuth2 DCR cleanup: removed %d stale application(s).", count)

api/oauth2_metadata/views.py

@@ -4,6 +4,15 @@
 from django.http import HttpRequest, JsonResponse
 from django.views.decorators.csrf import csrf_exempt
 from django.views.decorators.http import require_GET
+from rest_framework import status as drf_status
+from rest_framework.permissions import AllowAny
+from rest_framework.request import Request
+from rest_framework.response import Response
+from rest_framework.throttling import ScopedRateThrottle
+from rest_framework.views import APIView
+
+from oauth2_metadata.serializers import DCRRequestSerializer
+from oauth2_metadata.services import create_oauth2_application
 
 
 @csrf_exempt
@@ -35,3 +44,63 @@ def authorization_server_metadata(request: HttpRequest) -> JsonResponse:
     }
 
     return JsonResponse(metadata)
+
+
+class DynamicClientRegistrationView(APIView):
+    """RFC 7591 Dynamic Client Registration endpoint."""
+
+    authentication_classes: list[type] = []
+    permission_classes = [AllowAny]
+    throttle_classes = [ScopedRateThrottle]
+    throttle_scope = "dcr_register"
+
+    # Map DRF serializer field names to RFC 7591 error codes.
+    _rfc7591_error_codes: dict[str, str] = {
+        "redirect_uris": "invalid_redirect_uri",
+        "client_name": "invalid_client_metadata",
+        "grant_types": "invalid_client_metadata",
+        "response_types": "invalid_client_metadata",
+        "token_endpoint_auth_method": "invalid_client_metadata",
+    }
+
+    def post(self, request: Request) -> Response:
+        serializer = DCRRequestSerializer(data=request.data)
+        if not serializer.is_valid():
+            return self._rfc7591_error_response(serializer.errors)
+
+        data = serializer.validated_data
+
+        application = create_oauth2_application(
+            client_name=data["client_name"],
+            redirect_uris=data["redirect_uris"],
+        )
+
+        return Response(
+            {
+                "client_id": application.client_id,
+                "client_name": application.name,
+                "redirect_uris": data["redirect_uris"],
+                "grant_types": data["grant_types"],
+                "response_types": data["response_types"],
+                "token_endpoint_auth_method": data["token_endpoint_auth_method"],
+                "client_id_issued_at": int(application.created.timestamp()),
+            },
+            status=drf_status.HTTP_201_CREATED,
+        )
+
+    def _rfc7591_error_response(self, errors: dict[str, list[str]]) -> Response:
+        """Format validation errors per RFC 7591 section 3.2.2."""
+        first_field = next(iter(errors))
+        error_code = self._rfc7591_error_codes.get(
+            first_field, "invalid_client_metadata"
+        )
+        messages = errors[first_field]
+        description = messages[0] if isinstance(messages[0], str) else str(messages[0])
+
+        return Response(
+            {
+                "error": error_code,
+                "error_description": description,
+            },
+            status=drf_status.HTTP_400_BAD_REQUEST,
+        )