code: private HashMap<String, String> createTokenRequestHeaders(String grantCode) {
          JSONObject payload = new JSONObject();
          HashMap<String, String> headers;
          try {
              payload.put("code", grantCode);
  
              KeyPair keyPair = certificateStore.getStoredKeyPair();
              String jws = jsonSigner.sign(keyPair, payload);
  
              headers = new HashMap<>(1);
              headers.put("X-WL-Authenticate", jws);
  
          } catch (Exception e) {
              throw new RuntimeException("Failed to create token request headers", e);
          }
  
          return headers;
      }
docs: Generate the headers that will be used during the token request phase
  @param grantCode from the authorization phase
  @return Map with all the headers