With the authentication plugin set to clearpw_passthrouh, ldap users passed
through by maxscale are getting authenticated by xpand. But native xpand users
are not able to.

maxscale listner config:
==================
authenticator=pamauth
authenticator_options=pam_backend_mapping=clearpw_passthrough

client connection via maxscale
======================
[root@mcrae ~]# mysql --ssl -h mcrae -P 3307 -u xpanduser1 -ppassword
ERROR 1045 (HY000): [40960] Access denied: for user 'xpanduser1'@'10.2.12.190'
(using password: NO)

maxscale log:
==========
2023-07-31 11:00:37 info : (3) [MariaDBProtocol] Client from '10.2.12.190' is in progress of connecting to service 'Read-Only-Service' with SSL.
2023-07-31 11:00:37 info : (3) [MariaDBProtocol] Connection attributes: no attributes
2023-07-31 11:00:37 info : (3) [readconnroute] (Read-Only-Service); New session for server xpand1. Connections : 1
2023-07-31 11:00:37 info : (3) Started Read-Only-Service client session [3] for 'xpanduser1' from 10.2.12.190
2023-07-31 11:00:37 info : (3) Connected to 'xpand1' with thread id 318466
2023-07-31 11:00:37 error : (3) Authentication to 'xpand1' failed: 1045, #HY000: [40960] Access denied: for user 'xpanduser1'@'10.2.12.190' (using password: NO)
2023-07-31 11:00:37 error : (3) (Read-Only-Service); Authentication to 'xpand1' failed: 1045, #HY000: [40960] Access denied: for user 'xpanduser1'@'10.2.12.190' (using password: NO) (xpand1)
2023-07-31 11:00:37 info : (3) Stopped Read-Only-Service client session [3]
2023-07-31 11:00:37 info : Read 7 user@host entries from 'xpand1' for service 'Read-Only-Service'. The data was identical to existing user data.

Xpand log:
=======
2023-07-31 11:00:37.900626 UTC nid 2 oak012white.colo.sproutsys.com clxnode: INFO mysql/server/mysql_proto.c:180 auth_error(): Error authenticating Xpand user 'xpanduser1'@'10.2.12.190': Access denied: for user 'xpanduser1'@'10.2.12.190' (using password: NO)

With the above authentication settings we should allow both ldap and
native xpand users.