Identifying Origin with PAM/nsswitch

[CJ Bridges]

PAM and nsswitch typically appear to be used in tandem to manage  
logins on most Linux systems.

In a situation where a linux machine was configured to use "local nis  
ldap" for user authentication, the behavior when Joe tries to log in  
is (simplified):
Is Joe a local user?  Verify password if so.
If not local, is Joe an NIS user?  Verify password if so.
If not NIS, is Joe an LDAP user?  Verify password if so.

After that authentication procedure using the various PAM modules as  
appropriate, Joe has successfully logged in, and is working under an  
appropriate uid.

Later on, is there any way to figure out where Joe is really defined  
as a user, and/or how he logged in (via which module)?  getpwuid and  
friends would not appear to offer any distinction between the various  
user classes.

Thanks,
CJ Bridges