当pg_hba.conf文件配置的认证方法为md5，但服务端用户密码采用SCRAM加密时，服务端会自动采用SCRAM认证。

演示过程如下：

$  psql -c "SELECT rule_number,type,address,database,user_name,auth_method FROM pg_hba_file_rules;"
 rule_number | type  | address | database | user_name | auth_method 
-------------+-------+---------+----------+-----------+-------------
           1 | local |         | {all}    | {all}     | trust
           2 | host  | 0.0.0.0 | {all}    | {all}     | md5
(2 rows)

$ psql -h 192.168.20.200 -c "SELECT system_user,current_setting('password_encryption')"
Password for user postgres: 
 system_user  | current_setting 
--------------+-----------------
 md5:postgres | scram-sha-256
(1 row)

注：SQL查询里可以使用system_user来获取pg_hba.conf里配置的客户端认证方法。