static void addExtraProviders(Configuration conf,
    HashMap<Byte, SaslServerAuthenticationProvider> providers) {
    for (String implName : conf.getStringCollection(EXTRA_PROVIDERS_KEY)) {
      Class<?> clz;
      try {
        clz = Class.forName(implName);
      } catch (ClassNotFoundException e) {
        LOG.warn("Failed to find SaslServerAuthenticationProvider class {}", implName, e);
        continue;
      }

      if (!SaslServerAuthenticationProvider.class.isAssignableFrom(clz)) {
        LOG.warn("Server authentication class {} is not an instance of "
          + "SaslServerAuthenticationProvider", clz);
        continue;
      }

      try {
        SaslServerAuthenticationProvider provider =
          (SaslServerAuthenticationProvider) clz.getConstructor().newInstance();
        addProviderIfNotExists(provider, providers);
      } catch (InstantiationException | IllegalAccessException | NoSuchMethodException
        | InvocationTargetException e) {
        LOG.warn("Failed to instantiate {}", clz, e);
      }
    }
  }
Adds any providers defined in the configuration.
hbase-server/src/main/java/org/apache/hadoop/hbase/security/provider/SaslServerAuthenticationProviders.java