If firebird.conf on client side contains WireCrypt = Disabled and there is some problem with security DB for database being attached then client will get
Statement failed, SQLSTATE = 28000
Your user name and password are not defined.
-- regardless of AuthClient value on server (and client also).
Record with details of failure will be added into firebird.log only if WireCrypt != Disabled (i.e. is commented or assigned to 'Enabled').
Separate ticket was created after discuss with Alex (privately) about details of