We have a requirement that for login to the websphere's admin console,
instead of using default admin/admin credential , we have to use
something like SomeOtherUserName/SomePassword.

I achieved this by using standalone user registry (security > Secure
administration, applications, and infrastructure.> User account
repository > standalone user registry ) and I changed credentials in
the J2c Authentication data to the one I want. Credentials needed by
service integration buses have also been changed from admin/admin to
the needed one.

and now after restarting the websphere process server, I can login to
admin console using valid credential other than admin/admin. But the
problem which I am facing now is that when my websphere process server
starts up, the ltpaLoginModule is still using admin/admin credentials
for authentication and in my registry, I don't have any user with user
id as admin and hence my LTPA authentication is failing.

Can anybody tell me from where the ltpaLoginModule is picking up this
authentication information.
Thanks in advance.