Fix CORS by passing 'Origin' header to OAuthLib

It is possible to control CORS by overriding is_origin_allowed method
of RequestValidator class.
OAuthLib allows origin if:
- is_origin_allowed returns True for particular request
- Request connection is secure
- Request has 'Origin' header

tests/test_cors.py

@@ -0,0 +1,117 @@
+from urllib.parse import parse_qs, urlparse
+
+import pytest
+from django.contrib.auth import get_user_model
+from django.test import RequestFactory, TestCase
+from django.urls import reverse
+
+from oauth2_provider.models import get_application_model
+from oauth2_provider.oauth2_validators import OAuth2Validator
+
+from . import presets
+from .utils import get_basic_auth_header
+
+
+class CorsOAuth2Validator(OAuth2Validator):
+    def is_origin_allowed(self, client_id, origin, request, *args, **kwargs):
+        """Enable CORS in OAuthLib"""
+        return True
+
+
+Application = get_application_model()
+UserModel = get_user_model()
+
+CLEARTEXT_SECRET = "1234567890abcdefghijklmnopqrstuvwxyz"
+
+# CORS is allowed for https only
+CLIENT_URI = "https://example.org"
+
+
+@pytest.mark.usefixtures("oauth2_settings")
+@pytest.mark.oauth2_settings(presets.DEFAULT_SCOPES_RW)
+class CorsTest(TestCase):
+    """
+    Test that CORS headers can be managed by OAuthLib.
+    The objective is: http request 'Origin' header should be passed to OAuthLib
+    """
+
+    def setUp(self):
+        self.factory = RequestFactory()
+        self.test_user = UserModel.objects.create_user("test_user", "[email protected]", "123456")
+        self.dev_user = UserModel.objects.create_user("dev_user", "[email protected]", "123456")
+
+        self.oauth2_settings.ALLOWED_REDIRECT_URI_SCHEMES = ["https"]
+        self.oauth2_settings.PKCE_REQUIRED = False
+
+        self.application = Application.objects.create(
+            name="Test Application",
+            redirect_uris=(CLIENT_URI),
+            user=self.dev_user,
+            client_type=Application.CLIENT_CONFIDENTIAL,
+            authorization_grant_type=Application.GRANT_AUTHORIZATION_CODE,
+            client_secret=CLEARTEXT_SECRET,
+        )
+
+        self.oauth2_settings.ALLOWED_REDIRECT_URI_SCHEMES = ["https"]
+        self.oauth2_settings.OAUTH2_VALIDATOR_CLASS = CorsOAuth2Validator
+
+    def tearDown(self):
+        self.application.delete()
+        self.test_user.delete()
+        self.dev_user.delete()
+
+    def test_cors_header(self):
+        """
+        Test that /token endpoint has Access-Control-Allow-Origin
+        """
+        authorization_code = self._get_authorization_code()
+
+        # exchange authorization code for a valid access token
+        token_request_data = {
+            "grant_type": "authorization_code",
+            "code": authorization_code,
+            "redirect_uri": CLIENT_URI,
+        }
+
+        auth_headers = get_basic_auth_header(self.application.client_id, CLEARTEXT_SECRET)
+        auth_headers["origin"] = CLIENT_URI
+
+        response = self.client.post(reverse("oauth2_provider:token"), data=token_request_data, **auth_headers)
+        self.assertEqual(response.status_code, 200)
+        self.assertEqual(response["Access-Control-Allow-Origin"], CLIENT_URI)
+
+    def test_no_cors_header(self):
+        """
+        Test that /token endpoint does not have Access-Control-Allow-Origin
+        """
+        authorization_code = self._get_authorization_code()
+
+        # exchange authorization code for a valid access token
+        token_request_data = {
+            "grant_type": "authorization_code",
+            "code": authorization_code,
+            "redirect_uri": CLIENT_URI,
+        }
+
+        auth_headers = get_basic_auth_header(self.application.client_id, CLEARTEXT_SECRET)
+
+        response = self.client.post(reverse("oauth2_provider:token"), data=token_request_data, **auth_headers)
+        self.assertEqual(response.status_code, 200)
+        # No CORS headers, because request did not have Origin
+        self.assertFalse(response.has_header("Access-Control-Allow-Origin"))
+
+    def _get_authorization_code(self):
+        self.client.login(username="test_user", password="123456")
+
+        # retrieve a valid authorization code
+        authcode_data = {
+            "client_id": self.application.client_id,
+            "state": "random_state_string",
+            "scope": "read write",
+            "redirect_uri": "https://example.org",
+            "response_type": "code",
+            "allow": True,
+        }
+        response = self.client.post(reverse("oauth2_provider:authorize"), data=authcode_data)
+        query_dict = parse_qs(urlparse(response["Location"]).query)
+        return query_dict["code"].pop()