We have a SharePoint 2016 farm with both form-based authentication (FBA) and Active Directory Federated Services (ADFS) configured. This means that when unauthenticated users navigate to the site, they are first presented with a drop-down asking them what method they want to use to log-in: FBA or ADFS. The URL of this page (at least for us) is: https://mysharepointsite/_login/default.aspx
We have created a solution to customise this page, where we added our ocmpany logo and replace the dropdown with big buttons (touch friendly). However when deploying the solution at the moment we are replacing this /_login/default.aspx page, because I couldn't for the heck of me find a supported way to configure SharePoint to use an alternative page instead.
We know how to configure an alternative FBA log-in page (where users provide their username and password), but for the authentication provider selection page we're at a loss. Any ideas? Or there is no other wan other than replacing the file like we're doing?
We are concerned that replacing original out of the box files is not a great solution since they are likely to be overwritten by SharePoint updates.