(core) Google auth endpoint has not responded with auth code

Summary:
Google Auth popup wasn't able to resolve origin from gristConfig.
Moving this reponsability to server side, where it gets calculated from initial request.

Test Plan: n/a

Reviewers: dsagal, paulfitz

Reviewed By: paulfitz

Differential Revision: https://phab.getgrist.com/D2935

app/server/lib/sendAppPage.ts

@@ -51,12 +51,10 @@ export function makeGristConfig(homeUrl: string|null, extra: Partial<GristLoadCo
  * Primary used for Google Auth Grist's endpoint, but can be used in future in any other server side
  * authentication flow.
  */
-export function makeMessagePage(server: GristServer, staticDir: string) {
+export function makeMessagePage(staticDir: string) {
   return async (req: express.Request, resp: express.Response, message: any) => {
-    const config = server.getGristConfig();
     const fileContent = await fse.readFile(path.join(staticDir, "message.html"), 'utf8');
     const content = fileContent
-      .replace("<!-- INSERT CONFIG -->", `<script>window.gristConfig = ${JSON.stringify(config)};</script>`)
       .replace("<!-- INSERT MESSAGE -->", `<script>window.message = ${JSON.stringify(message)};</script>`);
     resp.status(200).type('html').send(content);
   };