code: public void login() {
          // first, let's see if we're running in a hadoop cluster and have the env configured
          boolean isHadoopCluster = isHadoopCluster();
          Configuration hadoopConfig = isHadoopCluster ? getHadoopConfiguration() : new Configuration(false);
          org.apache.commons.configuration.Configuration configuration = getApplicationConfiguration();
          if (!isHadoopCluster) {
              // need to read the configured authentication choice and create the UGI configuration
              setupHadoopConfiguration(hadoopConfig, configuration);
          }
          doServiceLogin(hadoopConfig, configuration);
      }
docs: Perform a SIMPLE login based on established OS identity or a kerberos based login using the configured
  principal and keytab (via atlas-application.properties).