docs: public void addCustomerSource(
              @NonNull String sourceId,
              @NonNull @Source.SourceType String sourceType,
              @Nullable SourceRetrievalListener listener) {
          final Map<String, Object> arguments = new HashMap<>();
          arguments.put(KEY_SOURCE, sourceId);
          arguments.put(KEY_SOURCE_TYPE, sourceType);
  
          final String operationId = UUID.randomUUID().toString();
          if (listener != null) {
              mSourceRetrievalListeners.put(operationId, listener);
          }
          mEphemeralKeyManager.retrieveEphemeralKey(operationId, ACTION_ADD_SOURCE, arguments);
      }