auth_saml: log mapping errors during user creation (#48784)

src/authentic2_auth_saml/adapters.py

@@ -74,6 +74,7 @@ class AuthenticAdapter(DefaultAdapter):
         try:
             self.provision_a2_attributes(user, idp, saml_attributes)
         except MappingError as e:
+            logger.warning('auth_saml: failure during attribute provisionning %s', e)
             raise UserCreationError('user creation failed on a mandatory mapping action: %s' % e)
         if not user.ou:
             user.ou = get_default_ou()