Choosing the authN backends depending on the cluent

[amolojo]

I would like to propose an enhancement to anvil connect.
This would be the possibility for anvil to propose a different login page depending on the client-id calling the /authorize endpoint.
This would allow Anvil to present different looking login pages (matching the looks of the caller in terms of UI), or to adapt the authN backend (for example, AD for employees and a different LDAP for partners).
This would require that the admin can associate specific providers and specific form templates to specific clients-ids
Ultimately, and for companies who have indeed several population authN backends, this would allow to put in place a single centralized HA anvil instance taking care of many apps seemlessly.