diff --git a/lib/handlers/http-message-user-infos-handler.js b/lib/handlers/http-message-user-infos-handler.js
new file mode 100644
--- /dev/null
+++ b/lib/handlers/http-message-user-infos-handler.js
@@ -0,0 +1,46 @@
+// @flow
+
+import _memoize from 'lodash/memoize.js';
+import t, { type TType } from 'tcomb';
+
+import type { CallSingleKeyserverEndpointResponse } from '../keyserver-conn/call-single-keyserver-endpoint.js';
+import { mixedRawThreadInfoValidator } from '../permissions/minimally-encoded-raw-thread-info-validators.js';
+import type { Endpoint } from '../types/endpoints.js';
+import { userInfoValidator } from '../types/user-types.js';
+import { endpointValidators } from '../types/validators/endpoint-validators.js';
+import { extractUserIDsFromPayload } from '../utils/conversion-utils.js';
+import { tID, tShape } from '../utils/validation-utils.js';
+
+function extendResponderValidatorBase(inputValidator: TType<*>): TType<*> {
+  return tShape({
+    ...inputValidator.meta.props,
+    cookieChange: t.maybe(
+      tShape({
+        threadInfos: t.dict(tID, mixedRawThreadInfoValidator),
+        userInfos: t.list(userInfoValidator),
+        cookieInvalidated: t.maybe(t.Boolean),
+        sessionID: t.maybe(t.String),
+        cookie: t.maybe(t.String),
+      }),
+    ),
+    error: t.maybe(t.String),
+    payload: t.maybe(t.Object),
+    success: t.maybe(t.Boolean),
+  });
+}
+
+const extendResponderValidator = _memoize(extendResponderValidatorBase);
+
+function extractAndPersistUserInfosFromEndpointResponse(
+  message: CallSingleKeyserverEndpointResponse,
+  endpoint: Endpoint,
+): void {
+  const extendedValidator = extendResponderValidator(
+    endpointValidators[endpoint].validator,
+  );
+  // eslint-disable-next-line no-unused-vars
+  const newUserIDs = extractUserIDsFromPayload(extendedValidator, message);
+  // TODO: dispatch an action adding the new user ids to the UserStore
+}
+
+export { extractAndPersistUserInfosFromEndpointResponse };