Due to some circumstances, one may have to bulkdelete all the OID users and reload them from AD to OID using the bootstrap process. Because it is a new bootstrap process, a new ORCLGUID may get generated in the OID that will make it out of sync with the target FND_USER.USER_GUID value. With such a scenario, Oracle will prompt again for the E-Business local username/pwd despite the system profile 'Applications SSO Auto Link User' having an 'Enabled' value. One can verify the mismatch after the reload by running the following command.
This orclguid shown above may NOT match the FND_USER.USER_GUID for the same user because the former is a newly generated one because of the reload process. In this case, Oracle prompts for the Oracle E-Business username/pwd after entering the Windows NT username/pwd in the login page even though the system profile 'Applications SSO Auto Link User' is set to 'Enabled', often confusing the user.
The process to 'auto link' SSO username and the FND_USER user_name after a reload of data from the 3rd party LDAP directory to OID is to update FND_USER.USER_GUID value to NULL.