amend to allow the callback url to use custom server ip and port as w…

…ell.

Note that this is required even in non-dockerized versions, e.g. when running RStudio-server from a cluster.  The dockerized sitation
is worse, in that HTTP_LOCALHOST must be set to 0.0.0.0, while the callback (HTTP_SERVER) must be set to the server's IP address instead.
In non-dockerized instances running on a server, both HTTP_LOCALHOST and HTTP_SERVER would simply be the server's IP

R/oauth-listener.r

@@ -75,7 +75,10 @@ oauth_listener <- function(request_url, is_interactive = interactive()) {
 #' @keywords internal
 #' @export
 oauth_callback <- function() {
-  "http://localhost:1410/"
+	paste0("http://", 
+               Sys.getenv("HTTR_SERVER", "localhost"),
+               ":",
+               Sys.getenv("HTTR_SERVER_PORT", "1410"))
 }
 
 listener_endpoint <- function() {