public String generate() {
    return generate(null);
  }
Generates the auth_to_local rules used by configuration settings such as core-site/auth_to_local.
<p/>
Each rule is concatenated using the default ConcatenationType, like calling
{@link #generate(ConcatenationType)} with {@link #DEFAULT_CONCATENATION_TYPE}

@return a string containing the generated auth-to-local rule set
ambari-server/src/main/java/org/apache/ambari/server/controller/AuthToLocalBuilder.java