This function is used to secure your Shiny app's server function. Make sure to pass
your Shiny app's server function as the first argument to secure_server() at
the bottom of your Shiny app's server.R file.
secure_server(server, custom_sign_in_server = NULL, custom_admin_server = NULL)a Shiny server function.
A Shiny server function (e.g function(input, output, session) {})
Either NULL, the default, or a Shiny server containing your custom
sign in server logic.
Either NULL, the default, or a Shiny server function containing your custom admin
server functionality.