DBTokenStore was initially introduced by
HIVE-3255 in Hive-0.12 and it is mainly for HMS delegation token. Later in Hive-0.13, the HS2 delegation token support was introduced by HIVE-5155 but it used MemoryTokenStore as token store. That the HIVE-9622 uses the shared RawStore (or HMSHandler) to access the token/keys information in HMS DB directly from HS2 seems not the right approach to support DBTokenStore in HS2. I think we should use HiveMetaStoreClient in HS2 instead.