Ok, so @erik-lonroth can we try this:
I think the gap is that you have to make sure that the controller knows about the user so we have to run the add-user command with the @corporate (or actually external?) user.
So I think the steps need to be
juju add-user USER@external
juju grant USER@external login
juju grant USER@external add-model
Then the user can
juju login 10.104.129.39:17070 -c iuba-vmware -u USER@external
Let me know how that goes for you. I think we’re close!