On premises web application and redirect url

I have a issue with redirect_url and a owin web application… I have a web application that is installed on a clients local web server. We are trying to allow them to login to this web application using Auth0 as our universal identity system. The problem is with the redirect_url, with our cloud based web application, setting the redirect_url is simple as there is only the one. However how can this be done for a installed web application? It would be best if I did not have to add something for EVERY installed local web application.
Do we need to add the redirect_url for each installed instance of the web application?
Do we have to have to add a new application for each instance of the installed application?

Is there anyway around this, I was planning on using the implicit flow, so I did not have to have a client secret on each installed web application, but I’m willing to change that if there is a easier path.