ldap: Tweak AUTH_LDAP_ADVANCED_REALM_ACCESS_CONTROL behavior.

The original behavior of this setting was to disable LDAP
authentication for any realms not configured to use it. This was an
arbitrary choice, and its only value was to potentially help catch
typos for users who are lazy about testing their configuration.

Since it makes it a very inconvenient to potentially host multiple
organizations with different LDAP configurations, remove that
behavior.

docs/overview/changelog.md

@@ -159,6 +159,12 @@ _Released 2023-11-16_
   various certain other special patterns are now forbidden. In the
   unlikely event that existing user groups have names matching these
   patterns, they will be automatically renamed on upgrade.
+- The behavior of the `AUTH_LDAP_ADVANCED_REALM_ACCESS_CONTROL` has
+  subtly changed. Previously, using this setting at all would block
+  LDAP authentication in organizations that are configured to use LDAP
+  authentication but not explicitly configured with advanced access
+  controls. This behavior was removed to simplify hosting multiple
+  organizations with different LDAP configuration preferences.
 
 ## Zulip Server 7.x series
 

docs/production/authentication-methods.md

@@ -435,9 +435,9 @@ organization's subdomain. The corresponding value is a list of
 `attribute: value` pair sets such that a user is permitted to access
 the organization if and only if the `attribute: value` pairs in at
 least one of these sets match the user's LDAP attributes. If this
-setting is enabled, organizations not explicitly configured in this
-setting will not be accessible via ldap authentication at all.
-
+setting is enabled, organizations not explicitly configured in it
+will not be affected - they'll allow normal LDAP login, unless restricted
+by other settings.
 This is better illustrated with an example:
 
 ```
@@ -457,8 +457,8 @@ AUTH_LDAP_ADVANCED_REALM_ACCESS_CONTROL = {
 This means that the organization `"zulip"` will be accessible via ldap
 authentication only for users whose ldap attributes either contain
 both `department: main` `employeeType: staff` or just `office:
-Dallas`. LDAP authentication will always fail for all other
-organizations in this configuration.
+Dallas`. LDAP authentication will proceed normally for all other
+organizations.
 
 :::{warning}
 Restricting access using these mechanisms only affects authentication via LDAP,

zerver/tests/test_auth_backends.py

@@ -4985,7 +4985,8 @@ class FetchAPIKeyTest(ZulipTestCase):
         self.assert_json_success(result)
         self.remove_ldap_user_attr("hamlet", "department")
 
-        # Test wrong configuration
+        # Test a realm that's not configured in the setting. Such a realm should not be affected,
+        # and just allow normal ldap login.
         with override_settings(
             AUTH_LDAP_ADVANCED_REALM_ACCESS_CONTROL={"not_zulip": [{"department": "zulip"}]}
         ):
@@ -4993,7 +4994,7 @@ class FetchAPIKeyTest(ZulipTestCase):
                 "/api/v1/fetch_api_key",
                 dict(username="hamlet", password=self.ldap_password("hamlet")),
             )
-            self.assert_json_error(result, "Your username or password is incorrect", 401)
+            self.assert_json_success(result)
 
     def test_inactive_user(self) -> None:
         do_deactivate_user(self.user_profile, acting_user=None)

zproject/backends.py

@@ -843,17 +843,18 @@ class ZulipLDAPAuthBackendBase(ZulipAuthMixin, LDAPBackend):
         # If neither setting is configured, allow access.
         if realm_access_control is None:
             return False
+        if realm.subdomain not in realm_access_control:
+            # If a realm is not configured in this setting, it shouldn't
+            # be affected by it - therefore, allow access.
+            return False
 
         # With settings.AUTH_LDAP_ADVANCED_REALM_ACCESS_CONTROL, we
         # allow access if and only if one of the entries for the
         # target subdomain matches the user's LDAP attributes.
-        if not (
-            realm.subdomain in realm_access_control
-            and isinstance(realm_access_control[realm.subdomain], list)
-            and len(realm_access_control[realm.subdomain]) > 0
-        ):
-            # If configuration is wrong, do not allow access
-            return True
+
+        # Make sure the format of the setting makes sense.
+        assert isinstance(realm_access_control[realm.subdomain], list)
+        assert len(realm_access_control[realm.subdomain]) > 0
 
         # Go through every "or" check
         for attribute_group in realm_access_control[realm.subdomain]: