Add IdentityServer3 Backend (#20275)

* Add IdentityServer3 Backend

This adds a backend for users who want to use IdentityServer3 as their
SSO provider. It can be used with the OAuth2ProviderConfig in django
admin to point to an external provider.

common/djangoapps/third_party_auth/identityserver3.py

+#pylint: disable=W0223
+"""
+    python-social-auth backend for use with IdentityServer3
+    docs: https://identityserver.github.io/Documentation/docsv2/endpoints/authorization.html
+    docs for adding a new backend to python-social-auth:
+    https://python-social-auth.readthedocs.io/en/latest/backends/implementation.html#oauth
+"""
+from social_core.backends.oauth import BaseOAuth2
+from django.utils.functional import cached_property
+
+
+class IdentityServer3(BaseOAuth2):
+    """
+    An extension of the BaseOAuth2 for use with an IdentityServer3 service.
+    """
+
+    name = "identityServer3"
+    REDIRECT_STATE = False
+    ACCESS_TOKEN_METHOD = 'POST'
+    DEFAULT_SCOPE = ['openid']
+    ID_KEY = "sub"
+
+    def authorization_url(self):
+        return self.get_config().get_setting('auth_url')
+
+    def access_token_url(self):
+        return self.get_config().get_setting('token_url')
+
+    def get_redirect_uri(self, state=None):
+        return self.get_config().get_setting('redirect_url')
+
+    def user_data(self, access_token, *args, **kwargs):
+        """
+        consumes the access_token to get data about the user logged
+        into the service.
+        """
+        url = self.get_config().get_setting('user_info_url')
+        # The access token returned from the service's token route.
+        header = {"Authorization": u"Bearer %s" % access_token}
+        return self.get_json(url, headers=header)
+
+    def get_user_details(self, response):
+        """
+        Return details about the user account from the service
+        """
+        details = {"fullname": response["name"], "email": response["email"]}
+        return details
+
+    def get_user_id(self, details, response):
+        """
+        Gets the unique identifier from the user. this is
+        how edx knows who's logging in, and if they have an account
+        already through edx. IdentityServer emits standard claim type of sub
+        to identify the user according to these docs:
+        https://openid.net/specs/openid-connect-core-1_0.html#StandardClaims
+        """
+        try:
+            user_id = response.get(self.ID_KEY)
+        except KeyError:
+            user_id = None
+        return user_id
+
+    def get_config(self):
+        return self._id3_config
+
+    @cached_property
+    def _id3_config(self):
+        from .models import OAuth2ProviderConfig
+        return OAuth2ProviderConfig.current("identityServer3")

common/djangoapps/third_party_auth/tests/test_identityserver3.py

+"""
+Unit tests for the IdentityServer3 OAuth2 Backend
+"""
+import unittest
+from third_party_auth.identityserver3 import IdentityServer3
+from third_party_auth.tests import testutil
+
+
+@unittest.skipUnless(testutil.AUTH_FEATURE_ENABLED, testutil.AUTH_FEATURES_KEY + ' not enabled')
+class IdentityServer3Test(testutil.TestCase):
+    """
+    Unit tests for the IdentityServer3 OAuth2 Backend
+    """
+
+    def setUp(self):
+        super(IdentityServer3Test, self).setUp()
+        self.id3_instance = IdentityServer3()
+
+    def test_proper_get_of_user_id(self):
+        """
+        make sure the "sub" claim works properly to grab user Id
+        """
+        response = {"sub": 1, "email": "example@example.com"}
+        self.assertEqual(self.id3_instance.get_user_id({}, response), 1)
+
+    def test_key_error_thrown_with_no_sub(self):
+        """
+        test that a KeyError is thrown if the "sub" claim does not exist
+        """
+        response = {"id": 1}
+        self.assertRaises(KeyError, self.id3_instance.get_user_id({}, response))
+
+    def test_proper_config_access(self):
+        """
+        test that the IdentityServer3 model properly grabs OAuth2Configs
+        """
+        provider_config = self.configure_identityServer3_provider(backend_name="identityServer3")
+        self.assertEqual(self.id3_instance.get_config(), provider_config)
+
+    def test_config_after_updating(self):
+        """
+        Make sure when the OAuth2Config for this backend is updated, the new config is properly grabbed
+        """
+        original_provider_config = self.configure_identityServer3_provider(enabled=True, slug="original")
+        updated_provider_config = self.configure_identityServer3_provider(
+            slug="updated",
+            backend_name="identityServer3"
+        )
+        self.assertEqual(self.id3_instance.get_config(), updated_provider_config)
+        self.assertNotEqual(self.id3_instance.get_config(), original_provider_config)

common/djangoapps/third_party_auth/tests/testutil.py

@@ -156,6 +156,12 @@ class ThirdPartyAuthTestMixin(object):
         kwargs.setdefault("backend_name", "dummy")
         return cls.configure_oauth_provider(**kwargs)
 
+    @classmethod
+    def configure_identityServer3_provider(cls, **kwargs):
+        kwargs.setdefault("name", "identityServer3TestConfig")
+        kwargs.setdefault("backend_name", "identityServer3")
+        return cls.configure_oauth_provider(**kwargs)
+
     @classmethod
     def verify_user_email(cls, email):
         """ Mark the user with the given email as verified """

lms/envs/production.py

@@ -678,6 +678,7 @@ if FEATURES.get('ENABLE_THIRD_PARTY_AUTH'):
         'social_core.backends.linkedin.LinkedinOAuth2',
         'social_core.backends.facebook.FacebookOAuth2',
         'social_core.backends.azuread.AzureADOAuth2',
+        'third_party_auth.identityserver3.IdentityServer3',
         'third_party_auth.saml.SAMLAuthBackend',
         'third_party_auth.lti.LTIAuthBackend',
     ])