Can anyone provide some ideas for solving the following issue?

Here are the constraints: 1) Using the latest AD provider for DNN 4.8.3, 2)confirmed the system can perform simple LDAP queries against TRUSTED DomainB, and DomainC using simple asp.net app(this verifies that the network and permissions allow this query to be performed) 3) DomainA is the domain that the webserver belongs to and has no issues.

How would I go about doing the following, lets say a user from Domain B already has an account created automatically the first time they visit the site(this is working fine). When that user wants to perform an AD forms based login they are unable to do so, I am thinking this does not work because the LDAP query is being performed against RootDSE or DomainA. In the same scenario a user from Domain A is able to perform an AD forms based login since the LDAP query is going against the domain that user belongs to...

I am hoping someone can point me to the right places in the AD provider code to make this change. I would be happy with something as simple as this:

If NetBiospartofUserName = DomainB then LDAP//DomainB

else NetBiospartofUserName = DomainC then LDAP//DomainC

else do normal LDAP//rootDSE ...

Thanks for any hints!