code: public List<String> getKeys(String prefix) {
          return IteratorUtils.toList(configuration.getKeys(prefix));
      }
docs: Get the list of the keys contained in the configuration that match the
  specified prefix. For instance, if the configuration contains the
  following keys:<br>
  {@code swagger2markup.extensions.folder1, swagger2markup.extensions.folder2, swagger2markup.folder3},<br>
  an invocation of {@code getKeys("swagger2markup.extensions");}<br>
  will return the key below:<br>
  {@code swagger2markup.extensions.folder1, swagger2markup.extensions.folder2}.<br>
  Note that the prefix itself is included in the result set if there is a
  matching key. The exact behavior - how the prefix is actually
  interpreted - depends on a concrete implementation.
  
  @param prefix The prefix to test against.
  @return the list of keys.