i tried:

# ldapwhoami
SASL/DIGEST-MD5 authentication started
Please enter your password:
ldap_sasl_interactive_bind_s: Invalid credentials (49)
additional info: SASL(-13): user not found: no secret in database

# ldapwhoami -x

this is interesting, but still I have the problem in the yast userinterface
is there an option within the yast - ldap server to change the authentication mode ?