Hi Trinetra,
SAP is a external application to LDAP. Changing of password in SAP should not change a user's LDAP password, because LDAP will be used for other application, like Outlook, portals, etc.So, password will not be changed for LDAP, for first or subsequent log ins
Now, there is only 1 user which is used for End user login page, i.e which is mentioned in service GRAC_UIBB_END_USER_LOGIN(SICF). So, when a user logs in to EUL, he/she logs in as the user specified in the above service. the authentication is however, as per Authentication Data Source config. in Maintain Data source config., which only checks whether the user exists in the Data Source.