You set the property once for each user. To delete a user, set that user's
password to null.
-- adding the user sa with password 'pass'
CALL SYSCS_UTIL.SYSCS_SET_DATABASE_PROPERTY(
'derby.user.sa', 'pass')
-- adding the user mary with password 'little7xylamb'
CALL SYSCS_UTIL.SYSCS_SET_DATABASE_PROPERTY(
'derby.user.mary', 'little7xylamb')
-- removing mary by setting password to null
CALL SYSCS_UTIL.SYSCS_SET_DATABASE_PROPERTY(
'derby.user.mary', null)