code: private String getKey(ServiceReference<AuthData> authDataRef) {
          String key = (String) authDataRef.getProperty(CFG_KEY_ID);
          if (key == null || DEFAULT_PATTERN.matcher(key).matches() || DEFAULT_NESTED_PATTERN.matcher(key).matches()) {
              key = (String) authDataRef.getProperty(CFG_KEY_DISPLAY_ID);
          }
          return key;
      }
docs: If the id was not specified (starts with default-), then use the config.displayId instead.
  The config admin assigns an id of the format default-n, where n is a number beginning at 0.
  For cardinality 1, 0, or -1, the value of n is 0. For multiple cardinality, the values are
  assigned sequentially starting with 0.
  
  @param authDataRef
  @return the key to use for saving the auth data configuration.