Change credential challenge to possession

Change-Id: Ib36ef7bfe8d879e0ae117f79a1aab52062184e68
diff --git a/src/requester-request-state.hpp b/src/requester-request-state.hpp
index af09012..9601b49 100644
--- a/src/requester-request-state.hpp
+++ b/src/requester-request-state.hpp
@@ -98,6 +98,10 @@
    */
   bool isNewlyCreatedIdentity = false;
   bool isNewlyCreatedKey = false;
+  /**
+   * @brief Store Nonce for signature
+   */
+  std::array<uint8_t, 16> nonce = {};
 };
 
 } // namespace requester