code: protected String getSigningKey() {
          if (extendedMetadata != null && extendedMetadata.getSigningKey() != null) {
              return extendedMetadata.getSigningKey();
          } else {
              return keyManager.getDefaultCredentialName();
          }
      }
docs: Provides key used for signing from extended metadata. Uses default key when key is not specified.
  
  @return signing key