Forward Auth (single application) Multiple domain

[indykoning]

Is your feature request related to a problem? Please describe.
When setting up Forward Auth for a single application you need to create a new provider per separate domain.
Which in general is good practice. However when dealing with multiple languages it can prove to be quote laborious for the same application.
E.g.:

• example.com
• example.nl
• example.net
• example.eu

All point to the same application, however due to the different domain you must create a new application and provider per domain.

Describe the solution you'd like
It would be nice to have an "Add entry" button for the external host(s) section of the proxy provider

Kind of like available in the OAuth2 provider with the redirect URi

Describe alternatives you've considered
Manually creating many applications and providers per domain which is currently the case.