feat: add support for app url variables (#915)

* feat: add support for app url variables

* fix: test not working

* fix: format issue

packages/auth/redirect.ts

@@ -1,5 +1,7 @@
 import type { ReadonlyHeaders } from "next/dist/server/web/spec-extension/adapters/headers";
 
+import { extractBaseUrlFromHeaders } from "@homarr/common";
+
 /**
  * The redirect_uri is constructed to work behind a reverse proxy. It is constructed from the headers x-forwarded-proto and x-forwarded-host.
  * @param headers
@@ -11,16 +13,9 @@ export const createRedirectUri = (headers: ReadonlyHeaders | null, pathname: str
     return pathname;
   }
 
-  let protocol = headers.get("x-forwarded-proto") ?? "http";
-
-  // @see https://support.glitch.com/t/x-forwarded-proto-contains-multiple-protocols/17219
-  if (protocol.includes(",")) {
-    protocol = protocol.includes("https") ? "https" : "http";
-  }
+  const baseUrl = extractBaseUrlFromHeaders(headers);
 
   const path = pathname.startsWith("/") ? pathname : `/${pathname}`;
 
-  const host = headers.get("x-forwarded-host") ?? headers.get("host");
-
-  return `${protocol}://${host}${path}`;
+  return `${baseUrl}${path}`;
 };