Allow using client_id as scope. Needed by B2C.

msal/application.py

@@ -588,18 +588,9 @@ def _decorate_scope(
             raise ValueError(
                 "API does not accept {} value as user-provided scopes".format(
                     reserved_scope))
-        if self.client_id in scope_set:
-            if len(scope_set) > 1:
-                # We make developers pass their client id, so that they can express
-                # the intent that they want the token for themselves (their own
-                # app).
-                # If we do not restrict them to passing only client id then they
-                # could write code where they expect an id token but end up getting
-                # access_token.
-                raise ValueError("Client Id can only be provided as a single scope")
-            decorated = set(reserved_scope)  # Make a writable copy
-        else:
-            decorated = scope_set | reserved_scope
+
+        # client_id can also be used as a scope in B2C
+        decorated = scope_set | reserved_scope
         decorated -= self._exclude_scopes
         return list(decorated)
 

tests/test_application.py

@@ -625,3 +625,18 @@ def test_organizations_authority_should_emit_warnning(self):
         self._test_certain_authority_should_emit_warnning(
             authority="https://login.microsoftonline.com/organizations")
 
+
+class TestScopeDecoration(unittest.TestCase):
+    def _test_client_id_should_be_a_valid_scope(self, client_id, other_scopes):
+        # B2C needs this https://learn.microsoft.com/en-us/azure/active-directory-b2c/access-tokens#openid-connect-scopes
+        reserved_scope = ['openid', 'profile', 'offline_access']
+        scopes_to_use = [client_id] + other_scopes
+        self.assertEqual(
+            set(ClientApplication(client_id)._decorate_scope(scopes_to_use)),
+            set(scopes_to_use + reserved_scope),
+            "Scope decoration should return input scopes plus reserved scopes")
+
+    def test_client_id_should_be_a_valid_scope(self):
+        self._test_client_id_should_be_a_valid_scope("client_id", [])
+        self._test_client_id_should_be_a_valid_scope("client_id", ["foo"])
+

tests/test_e2e.py

@@ -884,6 +884,18 @@ def test_b2c_acquire_token_by_ropc(self):
             scope=config["scopes"],
             )
 
+    def test_b2c_allows_using_client_id_as_scope(self):
+        # See also https://learn.microsoft.com/en-us/azure/active-directory-b2c/access-tokens#openid-connect-scopes
+        config = self.get_lab_app_object(azureenvironment="azureb2ccloud")
+        config["scopes"] = [config["appId"]]
+        self._test_username_password(
+            authority=self._build_b2c_authority("B2C_1_ROPC_Auth"),
+            client_id=config["appId"],
+            username="[email protected]",
+            password=self.get_lab_user_secret("msidlabb2c"),
+            scope=config["scopes"],
+            )
+
 
 class WorldWideRegionalEndpointTestCase(LabBasedTestCase):
     region = "westus"