The problem In PXC 5.6 and 5.7, when using xtrabackup-v2 as the SST method, the DBA must create a user with the appropriate privileges for use by Percona XtraBackup (PXB). The username and password of this backup user are specified in the wsrep_sst_auth variable. This is a problem because this username and password was being [&]

https://www.percona.com/blog/2019/10/03/percona-xtradb-cluster-8-0-new-feature-wsrep_sst_auth-removal/