public static synchronized SaslClientAuthenticationProviders getInstance(Configuration conf) {
    SaslClientAuthenticationProviders providers = providersRef.get();
    if (providers == null) {
      providers = instantiate(conf);
      providersRef.set(providers);
    }

    return providers;
  }
Returns a singleton instance of {@link SaslClientAuthenticationProviders}.
hbase-client/src/main/java/org/apache/hadoop/hbase/security/provider/SaslClientAuthenticationProviders.java