(core) when redirecting, use protocol in APP_HOME_URL if available

Summary:
Currently, Grist behind a reverse proxy will generate many
needless redirects via `http`, and can't be used with only
port 443. This diff centralizes generation of these redirects
and uses the protocol in APP_HOME_URL if it is set.

Test Plan:
manually tested by rebuilding grist-core and
doing a reverse proxy deployment that had no support for
port 80. Prior to this change, there are lots of problems;
after, the site works as expected.

Reviewers: jarek

Reviewed By: jarek

Differential Revision: https://phab.getgrist.com/D3400

app/server/lib/Authorizer.ts

@@ -15,7 +15,7 @@ import {COOKIE_MAX_AGE, getAllowedOrgForSessionID, getCookieDomain,
 import {makeId} from 'app/server/lib/idUtils';
 import * as log from 'app/server/lib/log';
 import {IPermitStore, Permit} from 'app/server/lib/Permit';
-import {allowHost, optStringParam} from 'app/server/lib/requestUtils';
+import {allowHost, getOriginUrl, optStringParam} from 'app/server/lib/requestUtils';
 import * as cookie from 'cookie';
 import {NextFunction, Request, RequestHandler, Response} from 'express';
 import {IncomingMessage} from 'http';
@@ -344,7 +344,7 @@ export function redirectToLoginUnconditionally(
     // logging out again, `users` will still be set.
     const signUp: boolean = (mreq.session.users === undefined);
     log.debug(`Authorizer: redirecting to ${signUp ? 'sign up' : 'log in'}`);
-    const redirectUrl = new URL(req.protocol + '://' + req.get('host') + req.originalUrl);
+    const redirectUrl = new URL(getOriginUrl(req) + req.originalUrl);
     if (signUp) {
       return resp.redirect(await getSignUpRedirectUrl(req, redirectUrl));
     } else {

app/server/lib/DiscourseConnect.ts

@@ -21,6 +21,7 @@
 import type {Express, NextFunction, Request, RequestHandler, Response} from 'express';
 import type {RequestWithLogin} from 'app/server/lib/Authorizer';
 import {expressWrap} from 'app/server/lib/expressWrap';
+import {getOriginUrl} from 'app/server/lib/requestUtils';
 import * as crypto from 'crypto';
 
 const DISCOURSE_CONNECT_SECRET = process.env.DISCOURSE_CONNECT_SECRET;
@@ -65,8 +66,8 @@ function discourseConnect(req: Request, resp: Response) {
     throw new Error('User is not authenticated');
   }
   if (!req.query.user && mreq.users && mreq.users.length > 1) {
-    const origUrl = new URL(req.originalUrl, `${req.protocol}://${req.get('host')}`);
-    const redirectUrl = new URL('/welcome/select-account', `${req.protocol}://${req.get('host')}`);
+    const origUrl = new URL(req.originalUrl, getOriginUrl(req));
+    const redirectUrl = new URL('/welcome/select-account', getOriginUrl(req));
     redirectUrl.searchParams.set('next', origUrl.toString());
     return resp.redirect(redirectUrl.toString());
   }

app/server/lib/FlexServer.ts

@@ -45,7 +45,8 @@ import {IPermitStore} from 'app/server/lib/Permit';
 import {getAppPathTo, getAppRoot, getUnpackedAppRoot} from 'app/server/lib/places';
 import {addPluginEndpoints, limitToPlugins} from 'app/server/lib/PluginEndpoint';
 import {PluginManager} from 'app/server/lib/PluginManager';
-import {adaptServerUrl, addOrgToPath, addPermit, getOrgUrl, getScope, optStringParam,
+import {
+  adaptServerUrl, addOrgToPath, addPermit, getOrgUrl, getOriginUrl, getScope, optStringParam,
         RequestWithGristInfo, stringParam, TEST_HTTPS_OFFSET, trustOrigin} from 'app/server/lib/requestUtils';
 import {ISendAppPageOptions, makeGristConfig, makeMessagePage, makeSendAppPage} from 'app/server/lib/sendAppPage';
 import {getDatabaseUrl} from 'app/server/lib/serverUtils';
@@ -1097,7 +1098,7 @@ export class FlexServer implements GristServer {
       const planRequired = task === 'signup' || task === 'updatePlan';
       if (!BillingTask.guard(task) || (planRequired && !req.query.billingPlan)) {
         // If the payment task/plan are invalid, redirect to the summary page.
-        return resp.redirect(req.protocol + '://' + req.get('host') + `/billing`);
+        return resp.redirect(getOriginUrl(req) + `/billing`);
       } else {
         return this._sendAppPage(req, resp, {path: 'billing.html', status: 200, config: {}});
       }
@@ -1519,7 +1520,7 @@ export class FlexServer implements GristServer {
   private _getOrgRedirectUrl(req: RequestWithLogin, subdomain: string, pathname: string = req.originalUrl): string {
     const config = this.getGristConfig();
     const {hostname, orgInPath} = getOrgUrlInfo(subdomain, req.get('host')!, config);
-    const redirectUrl = new URL(pathname, `${req.protocol}://${req.get('host')}`);
+    const redirectUrl = new URL(pathname, getOriginUrl(req));
     if (hostname) {
       redirectUrl.hostname = hostname;
     }

app/server/lib/SamlConfig.ts

@@ -61,6 +61,7 @@ import {expressWrap} from 'app/server/lib/expressWrap';
 import {GristLoginSystem, GristServer} from 'app/server/lib/GristServer';
 import * as log from 'app/server/lib/log';
 import {Permit} from 'app/server/lib/Permit';
+import {getOriginUrl} from 'app/server/lib/requestUtils';
 import {fromCallback} from 'app/server/lib/serverUtils';
 import {Sessions} from 'app/server/lib/Sessions';
 
@@ -156,7 +157,7 @@ export class SamlConfig {
 
     // Starting point for login. It redirects to the IdP, and then to /saml/assert.
     app.get("/saml/login", expressWrap(async (req, res, next) => {
-      res.redirect(await this.getLoginRedirectUrl(req, new URL(req.protocol + "://" + req.get('host'))));
+      res.redirect(await this.getLoginRedirectUrl(req, new URL(getOriginUrl(req))));
     }));
 
     // Assert endpoint for when the login completes as POST.

app/server/lib/extractOrg.ts

@@ -3,6 +3,7 @@ import { mapGetOrSet, MapWithTTL } from 'app/common/AsyncCreate';
 import { extractOrgParts, getHostType, getKnownOrg } from 'app/common/gristUrls';
 import { Organization } from 'app/gen-server/entity/Organization';
 import { HomeDBManager } from 'app/gen-server/lib/HomeDBManager';
+import { getOriginUrl } from 'app/server/lib/requestUtils';
 import { NextFunction, Request, RequestHandler, Response } from 'express';
 import { IncomingMessage } from 'http';
 
@@ -155,7 +156,7 @@ export class Hosts {
         return o && o.host || undefined;
       });
       if (orgHost && orgHost !== req.hostname) {
-        const url = new URL(`${req.protocol}://${req.headers.host}${req.path}`);
+        const url = new URL(getOriginUrl(req) + req.path);
         url.hostname = orgHost;  // assigning hostname rather than host preserves port.
         return resp.redirect(url.href);
       }

app/server/lib/requestUtils.ts

@@ -70,7 +70,7 @@ export function addOrgToPath(req: RequestWithOrg, path: string): string {
  * Get url to the org associated with the request.
  */
 export function getOrgUrl(req: Request, path: string = '/') {
-  return req.protocol + '://' + req.get('host') + addOrgToPathIfNeeded(req, path);
+  return getOriginUrl(req) + addOrgToPathIfNeeded(req, path);
 }
 
 /**
@@ -97,8 +97,8 @@ export function trustOrigin(req: Request, resp: Response): boolean {
 // enough if only the base domains match. Differing ports are allowed, which helps in dev/testing.
 export function allowHost(req: Request, allowedHost: string|URL) {
   const mreq = req as RequestWithOrg;
-  const proto = req.protocol;
-  const actualUrl = new URL(`${proto}://${req.get('host')}`);
+  const proto = getEndUserProtocol(req);
+  const actualUrl = new URL(getOriginUrl(req));
   const allowedUrl = (typeof allowedHost === 'string') ? new URL(`${proto}://${allowedHost}`) : allowedHost;
   if (mreq.isCustomHost) {
     // For a request to a custom domain, the full hostname must match.
@@ -282,11 +282,24 @@ export interface RequestWithGristInfo extends Request {
  * https://docs.aws.amazon.com/elasticloadbalancing/latest/classic/x-forwarded-headers.html
  */
 export function getOriginUrl(req: Request) {
-  const host = req.headers.host!;
-  const protocol = req.get("X-Forwarded-Proto") || req.protocol;
+  const host = req.get('host')!;
+  const protocol = getEndUserProtocol(req);
   return `${protocol}://${host}`;
 }
 
+/**
+ * Get the protocol to use in Grist URLs that are intended to be reachable
+ * from a user's browser. Use the protocol in APP_HOME_URL if available,
+ * otherwise X-Forwarded-Proto is set on the provided request, otherwise
+ * the protocol of the request itself.
+ */
+export function getEndUserProtocol(req: Request) {
+  if (process.env.APP_HOME_URL) {
+    return new URL(process.env.APP_HOME_URL).protocol.replace(':', '');
+  }
+  return req.get("X-Forwarded-Proto") || req.protocol;
+}
+
 /**
  * In some configurations, session information may be cached by the server.
  * When session information changes, give the server a chance to clear its