From 8841c0bfec195f5a1c5aefe379a34af4a59432ef Mon Sep 17 00:00:00 2001
From: Raphael Lullis <raphael@mushroomlabs.com>
Date: Fri, 2 May 2025 01:21:08 +0200
Subject: [PATCH] Add support for RP-Initiated Registration

By adding a `prompt=create` parameter to the authorization request,
the user is redirected to the OP's registration point where they
can create an account, and on successful registration the user is
then redirected back to the authorization view with prompt=login

Closes #1546
---
 AUTHORS                       |  1 +
 CHANGELOG.md                  |  1 +
 docs/settings.rst             | 19 ++++++++
 oauth2_provider/settings.py   |  2 +
 oauth2_provider/views/base.py | 70 +++++++++++++++++++++++++++-
 oauth2_provider/views/oidc.py |  4 ++
 tests/presets.py              |  4 ++
 tests/test_oidc_views.py      | 87 ++++++++++++++++++++++++++++++++++-
 8 files changed, 185 insertions(+), 3 deletions(-)

diff --git a/AUTHORS b/AUTHORS
index 2d3f80527..90271a635 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -100,6 +100,7 @@ Peter Karman
 Peter McDonald
 Petr Dlouhý
 pySilver
+Raphael Lullis
 Rodney Richardson
 Rustem Saiargaliev
 Rustem Saiargaliev
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 32dd1734c..89268f8f0 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Added
 * #1506 Support for Wildcard Origin and Redirect URIs
 * #1586 Turkish language support added
+* #1546 Support for RP-Initiated Registration
 
 <!--
 ### Changed
diff --git a/docs/settings.rst b/docs/settings.rst
index 985ca5d2c..90aa6a74c 100644
--- a/docs/settings.rst
+++ b/docs/settings.rst
@@ -353,6 +353,7 @@ this you must also provide the service at that endpoint.
 If unset, the default location is used, eg if ``django-oauth-toolkit`` is
 mounted at ``/o/``, it will be ``<server-address>/o/userinfo/``.
 
+
 OIDC_RP_INITIATED_LOGOUT_ENABLED
 ~~~~~~~~~~~~~~~~~~~~~~~~
 Default: ``False``
@@ -388,6 +389,24 @@ Whether to delete the access, refresh and ID tokens of the user that is being lo
 The types of applications for which tokens are deleted can be customized with ``RPInitiatedLogoutView.token_types_to_delete``.
 The default is to delete the tokens of all applications if this flag is enabled.
 
+OIDC_RP_INITIATED_REGISTRATION_ENABLED
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Default: ``False``
+
+Whether to allow the Relying Party (RP) to direct a user to an OpenID
+Provider (OP) to create a new account rather than authenticate with an
+existing one. This is done by adding a `prompt=create` parameter to
+the authorization request.
+
+OIDC_RP_INITIATED_REGISTRATION_VIEW_NAME
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Default: ''
+
+The name of the view for the URL that the user will be redirected to
+in case RP-Initated Registration is enabled.
+
+
+
 OIDC_ISS_ENDPOINT
 ~~~~~~~~~~~~~~~~~
 Default: ``""``
diff --git a/oauth2_provider/settings.py b/oauth2_provider/settings.py
index 9771aa4e7..bbda2c540 100644
--- a/oauth2_provider/settings.py
+++ b/oauth2_provider/settings.py
@@ -92,6 +92,8 @@
         "client_secret_post",
         "client_secret_basic",
     ],
+    "OIDC_RP_INITIATED_REGISTRATION_ENABLED": False,
+    "OIDC_RP_INITIATED_REGISTRATION_VIEW_NAME": None,
     "OIDC_RP_INITIATED_LOGOUT_ENABLED": False,
     "OIDC_RP_INITIATED_LOGOUT_ALWAYS_PROMPT": True,
     "OIDC_RP_INITIATED_LOGOUT_STRICT_REDIRECT_URIS": False,
diff --git a/oauth2_provider/views/base.py b/oauth2_provider/views/base.py
index c5c904b14..c02e551e9 100644
--- a/oauth2_provider/views/base.py
+++ b/oauth2_provider/views/base.py
@@ -1,12 +1,14 @@
 import hashlib
 import json
 import logging
-from urllib.parse import parse_qsl, urlencode, urlparse
+from urllib.parse import parse_qsl, quote, urlencode, urlparse
 
 from django.contrib.auth.mixins import LoginRequiredMixin
 from django.contrib.auth.views import redirect_to_login
-from django.http import HttpResponse
+from django.http import HttpResponse, HttpResponseBadRequest, HttpResponseRedirect
 from django.shortcuts import resolve_url
+from django.urls import reverse
+from django.urls.exceptions import NoReverseMatch
 from django.utils import timezone
 from django.utils.decorators import method_decorator
 from django.views.decorators.csrf import csrf_exempt
@@ -154,6 +156,8 @@ def get(self, request, *args, **kwargs):
         prompt = request.GET.get("prompt")
         if prompt == "login":
             return self.handle_prompt_login()
+        elif prompt == "create":
+            return self.handle_prompt_create()
 
         all_scopes = get_scopes_backend().get_all_scopes()
         kwargs["scopes_descriptions"] = [all_scopes[scope] for scope in scopes]
@@ -252,6 +256,63 @@ def handle_prompt_login(self):
             self.get_redirect_field_name(),
         )
 
+    def handle_prompt_create(self):
+        """
+        When prompt=create is in the authorization request,
+        redirect the user to the registration page. After
+        registration, the user should be redirected back to the
+        authorization endpoint without the prompt parameter to
+        continue the OIDC flow.
+
+        Implements OpenID Connect Prompt Create 1.0 specification.
+        https://openid.net/specs/openid-connect-prompt-create-1_0.html
+
+        """
+        try:
+            assert not self.request.user.is_authenticated, "account_selection_required"
+            path = self.request.build_absolute_uri()
+
+            views_to_attempt = [oauth2_settings.OIDC_RP_INITIATED_REGISTRATION_VIEW_NAME, "account_signup"]
+
+            registration_url = None
+            for view_name in views_to_attempt:
+                try:
+                    registration_url = reverse(view_name)
+                    continue
+                except NoReverseMatch:
+                    pass
+
+            # Parse the current URL and remove the prompt parameter
+            parsed = urlparse(path)
+            parsed_query = dict(parse_qsl(parsed.query))
+            parsed_query.pop("prompt")
+
+            # Create the next parameter to redirect back to the authorization endpoint
+            next_url = parsed._replace(query=urlencode(parsed_query)).geturl()
+
+            assert oauth2_settings.OIDC_RP_INITIATED_REGISTRATION_ENABLED, "access_denied"
+            assert registration_url is not None, "access_denied"
+
+            # Add next parameter to registration URL
+            separator = "&" if "?" in registration_url else "?"
+            redirect_to = f"{registration_url}{separator}next={quote(next_url)}"
+
+            return HttpResponseRedirect(redirect_to)
+
+        except AssertionError as exc:
+            redirect_uri = self.request.GET.get("redirect_uri")
+            if redirect_uri:
+                response_parameters = {"error": str(exc)}
+                state = self.request.GET.get("state")
+                if state:
+                    response_parameters["state"] = state
+
+                separator = "&" if "?" in redirect_uri else "?"
+                redirect_to = redirect_uri + separator + urlencode(response_parameters)
+                return self.redirect(redirect_to, application=None)
+            else:
+                return HttpResponseBadRequest(str(exc))
+
     def handle_no_permission(self):
         """
         Generate response for unauthorized users.
@@ -259,6 +320,8 @@ def handle_no_permission(self):
         If prompt is set to none, then we redirect with an error code
         as defined by OIDC 3.1.2.6
 
+        If prompt is set to create, then we redirect to the registration page.
+
         Some code copied from OAuthLibMixin.error_response, but that is designed
         to operated on OAuth1Error from oauthlib wrapped in a OAuthToolkitError
         """
@@ -276,6 +339,9 @@ def handle_no_permission(self):
             separator = "&" if "?" in redirect_uri else "?"
             redirect_to = redirect_uri + separator + urlencode(response_parameters)
             return self.redirect(redirect_to, application=None)
+        elif prompt == "create":
+            # If prompt=create and user is not authenticated, redirect to registration
+            return self.handle_prompt_create()
         else:
             return super().handle_no_permission()
 
diff --git a/oauth2_provider/views/oidc.py b/oauth2_provider/views/oidc.py
index a252f1be4..eb70947f9 100644
--- a/oauth2_provider/views/oidc.py
+++ b/oauth2_provider/views/oidc.py
@@ -100,7 +100,11 @@ def get(self, request, *args, **kwargs):
             ),
             "code_challenge_methods_supported": [key for key, _ in AbstractGrant.CODE_CHALLENGE_METHODS],
             "claims_supported": oidc_claims,
+            "prompt_values_supported": ["none", "login"],
         }
+        if oauth2_settings.OIDC_RP_INITIATED_REGISTRATION_ENABLED:
+            data["prompt_values_supported"].append("create")
+
         if oauth2_settings.OIDC_RP_INITIATED_LOGOUT_ENABLED:
             data["end_session_endpoint"] = end_session_endpoint
         response = JsonResponse(data)
diff --git a/tests/presets.py b/tests/presets.py
index 4538c64eb..0fe04dd74 100644
--- a/tests/presets.py
+++ b/tests/presets.py
@@ -37,6 +37,10 @@
 OIDC_SETTINGS_RP_LOGOUT_DENY_EXPIRED["OIDC_RP_INITIATED_LOGOUT_ACCEPT_EXPIRED_TOKENS"] = False
 OIDC_SETTINGS_RP_LOGOUT_KEEP_TOKENS = deepcopy(OIDC_SETTINGS_RP_LOGOUT)
 OIDC_SETTINGS_RP_LOGOUT_KEEP_TOKENS["OIDC_RP_INITIATED_LOGOUT_DELETE_TOKENS"] = False
+OIDC_SETTINGS_RP_REGISTRATION = deepcopy(OIDC_SETTINGS_RW)
+OIDC_SETTINGS_RP_REGISTRATION["OIDC_RP_INITIATED_REGISTRATION_ENABLED"] = True
+OIDC_SETTINGS_RP_REGISTRATION["OIDC_RP_INITIATED_REGISTRATION_VIEW_NAME"] = "testapp:register"
+
 REST_FRAMEWORK_SCOPES = {
     "SCOPES": {
         "read": "Read scope",
diff --git a/tests/test_oidc_views.py b/tests/test_oidc_views.py
index 65197cbd1..238ddf565 100644
--- a/tests/test_oidc_views.py
+++ b/tests/test_oidc_views.py
@@ -1,3 +1,6 @@
+from unittest.mock import patch
+from urllib.parse import parse_qs, urlparse
+
 import pytest
 from django.contrib.auth import get_user
 from django.contrib.auth.models import AnonymousUser
@@ -12,7 +15,12 @@
     InvalidOIDCClientError,
     InvalidOIDCRedirectURIError,
 )
-from oauth2_provider.models import get_access_token_model, get_id_token_model, get_refresh_token_model
+from oauth2_provider.models import (
+    get_access_token_model,
+    get_application_model,
+    get_id_token_model,
+    get_refresh_token_model,
+)
 from oauth2_provider.oauth2_validators import OAuth2Validator
 from oauth2_provider.settings import oauth2_settings
 from oauth2_provider.views.oidc import RPInitiatedLogoutView, _load_id_token, _validate_claims
@@ -47,6 +55,7 @@ def test_get_connect_discovery_info(self):
             "token_endpoint_auth_methods_supported": ["client_secret_post", "client_secret_basic"],
             "code_challenge_methods_supported": ["plain", "S256"],
             "claims_supported": ["sub"],
+            "prompt_values_supported": ["none", "login"],
         }
         response = self.client.get("/o/.well-known/openid-configuration")
         self.assertEqual(response.status_code, 200)
@@ -74,6 +83,7 @@ def test_get_connect_discovery_info_deprecated(self):
             "token_endpoint_auth_methods_supported": ["client_secret_post", "client_secret_basic"],
             "code_challenge_methods_supported": ["plain", "S256"],
             "claims_supported": ["sub"],
+            "prompt_values_supported": ["none", "login"],
         }
         response = self.client.get("/o/.well-known/openid-configuration/")
         self.assertEqual(response.status_code, 200)
@@ -101,6 +111,7 @@ def expect_json_response_with_rp_logout(self, base):
             "token_endpoint_auth_methods_supported": ["client_secret_post", "client_secret_basic"],
             "code_challenge_methods_supported": ["plain", "S256"],
             "claims_supported": ["sub"],
+            "prompt_values_supported": ["none", "login"],
             "end_session_endpoint": f"{base}/logout/",
         }
         response = self.client.get(reverse("oauth2_provider:oidc-connect-discovery-info"))
@@ -135,6 +146,7 @@ def test_get_connect_discovery_info_without_issuer_url(self):
             "token_endpoint_auth_methods_supported": ["client_secret_post", "client_secret_basic"],
             "code_challenge_methods_supported": ["plain", "S256"],
             "claims_supported": ["sub"],
+            "prompt_values_supported": ["none", "login"],
         }
         response = self.client.get(reverse("oauth2_provider:oidc-connect-discovery-info"))
         self.assertEqual(response.status_code, 200)
@@ -206,6 +218,79 @@ def test_get_jwks_info_multiple_rsa_keys(self):
         assert response.json() == expected_response
 
 
+@pytest.mark.usefixtures("oauth2_settings")
+@pytest.mark.oauth2_settings(presets.OIDC_SETTINGS_RP_REGISTRATION)
+class TestRPInitiatedRegistration(TestCase):
+    def test_connect_discovery_info_has_create(self):
+        expected_response = {
+            "issuer": "http://localhost/o",
+            "authorization_endpoint": "http://localhost/o/authorize/",
+            "token_endpoint": "http://localhost/o/token/",
+            "userinfo_endpoint": "http://localhost/o/userinfo/",
+            "jwks_uri": "http://localhost/o/.well-known/jwks.json",
+            "scopes_supported": ["read", "write", "openid"],
+            "response_types_supported": [
+                "code",
+                "token",
+                "id_token",
+                "id_token token",
+                "code token",
+                "code id_token",
+                "code id_token token",
+            ],
+            "subject_types_supported": ["public"],
+            "id_token_signing_alg_values_supported": ["RS256", "HS256"],
+            "token_endpoint_auth_methods_supported": ["client_secret_post", "client_secret_basic"],
+            "code_challenge_methods_supported": ["plain", "S256"],
+            "claims_supported": ["sub"],
+            "prompt_values_supported": ["none", "login", "create"],
+        }
+        response = self.client.get("/o/.well-known/openid-configuration")
+        self.assertEqual(response.status_code, 200)
+        assert response.json() == expected_response
+
+    def test_prompt_create_redirects_to_registration_view(self):
+        Application = get_application_model()
+        application = Application.objects.create(
+            name="Test Application",
+            redirect_uris="http://localhost http://example.com",
+            client_type=Application.CLIENT_CONFIDENTIAL,
+            authorization_grant_type=Application.GRANT_AUTHORIZATION_CODE,
+        )
+
+        auth_url = reverse("oauth2_provider:authorize")
+        query_params = {
+            "response_type": "code",
+            "client_id": application.client_id,
+            "redirect_uri": "http://localhost",
+            "scope": "openid",
+            "prompt": "create",
+        }
+
+        with patch("oauth2_provider.views.base.reverse") as patched_reverse:
+            patched_reverse.return_value = "/register-test/"
+            response = self.client.get(f"{auth_url}?{'&'.join(f'{k}={v}' for k, v in query_params.items())}")
+
+        self.assertEqual(response.status_code, 302)
+        redirect_url = response.url
+        parsed_url = urlparse(redirect_url)
+
+        # Verify it's the registration URL
+        self.assertEqual(parsed_url.path, "/register-test/")
+
+        # Verify the query parameters
+        query = parse_qs(parsed_url.query)
+        self.assertIn("next", query)
+
+        # Verify the next parameter doesn't contain prompt=create
+        next_url = query["next"][0]
+        self.assertNotIn("prompt=create", next_url)
+
+        # But it should contain the other original parameters
+        self.assertIn("response_type=code", next_url)
+        self.assertIn(f"client_id={application.client_id}", next_url)
+
+
 def mock_request():
     """
     Dummy request with an AnonymousUser attached.