You receive "Application error" or "Cannot redirect an HTTPS request to an HTTP virtual URL" errors in a reverse proxy deployment using form-based authentication.
Form IP and Form Cookie use a virtual URL to redirect the user to an URL with the authentication from. This virtual URL must resolve to the proxy IP in the client DNS.
If the proxy is intercepting traffic for a Web server, use the Web server URL as the virtual URL. It will resolve to the proxy IP and work for users outside the organization with public DNS servers. If the Web server URL is HTTPS, the virtual URL must be HTTPS.