The problem of implementing oauth2.0 with spring cloud

recently studied the use of Spring cloud. The security framework intends to use oauth2.0, but there are some problems that I don"t quite understand.

1. What is the function of ClientDetailsService?
2. TokenStore is the place where token is saved. Does oauth2.0 have to save token?
3. If you are using JwtTokenStore, why does jwt need to be saved?
4. What is the whole process if you use TokenEnhancer of RedisTokenStore + Jwt?

Apr.07,2022
MySQL Query : SELECT * FROM `codeshelper`.`v9_news` WHERE status=99 AND catid='6' ORDER BY rand() LIMIT 5
MySQL Error : Disk full (/tmp/#sql-temptable-64f5-1b3e219-347b5.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1b3e219-347b5.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
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