Use custom socialaccount adapter to accommodate LDAP backend

The LDAP backend does not set a usable password in Django, which
triggers a saftey net in allauth when trying to disconnect the last
social auth method.

aleksis/core/util/auth_helpers.py

+"""Helpers/overrides for django-allauth."""
+
+from django.conf import settings
+
+from allauth.socialaccount.adapter import DefaultSocialAccountAdapter
+
+
+class OurSocialAccountAdapter(DefaultSocialAccountAdapter):
+    """Customised adapter that recognises other authentication mechanisms."""
+
+    def validate_disconnect(self, account, accounts):
+        """Validate whether or not the socialaccount account can be safely disconnected.
+
+        Honours other authentication backends, i.e. ignores unusable passwords if LDAP is used.
+        """
+        if "django_auth_ldap.backend.LDAPBackend" in settings.AUTHENTICATION_BACKENDS:
+            # Ignore upstream validation error as we do not need a usable password
+            return None
+
+        # Let upstream decide whether we can disconnect or not
+        return super().validate_disconnect(account, accounts)