My institution has 4 domains all with a trust relationship between them. Can I have multiple LDAP servers (1 for each domain) so authentication can occur setup in the AuthLDAP? Or is there a better way to do the setup. Currently, if I put 1 of the domains ldap info in, and search for a user in that domain, it works, but it won't find users in other domains.

Not in core AuthLDAP plugin.

But it's great : it's a public plugin, then you can create a new one based on this code

Just rename it to multipleAuthLDAP and for starting : put the config as a fixed array in the file