I've switched a Webforms app from Forms Authentication to Azure AD B2C using MSAL.NET. That works fine but I'm having trouble getting it to serve a Default Document.
In Forms Authentication the config has a setting for the login page and a setting for the page to redirect to once the user has authenticated. We use the login page to accept credentials and act as branded splash page. In MSAL there are equivalents but the login page is hosted by Azure. So if I load www.example.com it will redirect straight to the Azure login page. What I want it to do is load a splash page or pre-login page from which the user initiates the redirect to the Azure login page. I could customise the Azure login page but ideally want this splash page within the web app.
Setting a defaultDocument in the web.config doesn't work, presumably because its using the Owin pipeline, neither does setting CookieAuthenticationOptions.LoginPath when adding the cookie authentication middleware.
Has anybody got a solution for this please?