OIDC issuer behind a proxy cannot be accessed about grist-core HOT 4 OPEN

import { ProxyAgent } from 'proxy-agent';
// The correct proxy `Agent` implementation to use will be determined
// via the `http_proxy` / `https_proxy` / `no_proxy` / etc. env vars
const agent = new ProxyAgent();

import { custom } from 'openid-client';
client[custom.http_options] = function (url, options) {
  const result = {};
  // use HTTP(S)_PROXY
  // https://nodejs.org/api/http.html#httprequesturl-options-callback
  // e.g. using https://www.npmjs.com/package/proxy-agent
  result.agent = agent;

  return result;
}

diff --git a/app/server/lib/OIDCConfig.ts b/app/server/lib/OIDCConfig.ts
index 86f78bce..9f9e78ee 100644
--- a/app/server/lib/OIDCConfig.ts
+++ b/app/server/lib/OIDCConfig.ts
@@ -52,12 +52,13 @@
 
 import * as express from 'express';
 import { GristLoginSystem, GristServer } from './GristServer';
-import { Client, generators, Issuer, UserinfoResponse } from 'openid-client';
+import { Client, generators, Issuer, UserinfoResponse, custom } from 'openid-client';
 import { Sessions } from './Sessions';
 import log from 'app/server/lib/log';
 import { appSettings } from './AppSettings';
 import { RequestWithLogin } from './Authorizer';
 import { UserProfile } from 'app/common/LoginSessionAPI';
+import { ProxyAgent } from 'proxy-agent';
 
 const CALLBACK_URL = '/oauth2/callback';
 
@@ -121,6 +122,12 @@ export class OIDCConfig {
       redirect_uris: [ this._redirectUrl ],
       response_types: [ 'code' ],
     });
+    this._client[custom.http_options] = function(url, options) {
+           // use HTTP(S)_PROXY env vars
+           // https://nodejs.org/api/http.html#httprequesturl-options-callback
+           const agent = new ProxyAgent();
+           return { agent };
+    }
     if (this._client.issuer.metadata.end_session_endpoint === undefined &&
         !this._endSessionEndpoint && !this._skipEndSessionEndpoint) {
       throw new Error('The Identity provider does not propose end_session_endpoint. ' +
diff --git a/package.json b/package.json
index bbe1c5e5..c6d83c88 100644
--- a/package.json
+++ b/package.json
@@ -182,6 +182,7 @@
     "popper-max-size-modifier": "0.2.0",
     "popweasel": "0.1.20",
     "prom-client": "14.2.0",
+    "proxy-agent": "6.4.0",