@VisibleForTesting
  synchronized static void shutdown() {
    INSTANCE = null;
  }
A token is generated when the SAML assertion is successfully validated. This Token
is passed back to the client (Jdbc/ODBC Driver) via the browser. This token is
presented by the subsequent http request as a bearer token.
service/src/java/org/apache/hive/service/auth/saml/HiveSamlAuthTokenGenerator.java