https: make https.globalAgent overridable also under ECMAScript Modules

Under ECMAScript modules when you do "import * as https from 'https'"
you get a new object with properties copied from https module exports.
So if this is a regular data property, you will just override a copy,
but if this would be a accessor property, we can still access the actual
https.globalAgent.

Refs: nodejs#25170, nodejs#9386

lib/https.js

@@ -30,6 +30,7 @@ const {
   FunctionPrototypeCall,
   JSONStringify,
   ObjectAssign,
+  ObjectDefineProperty,
   ObjectSetPrototypeOf,
   ReflectApply,
   ReflectConstruct,
@@ -350,7 +351,7 @@ Agent.prototype._evictSession = function _evictSession(key) {
   delete this._sessionCache.map[key];
 };
 
-const globalAgent = new Agent({ keepAlive: true, scheduling: 'lifo', timeout: 5000 });
+let globalAgent = new Agent({ keepAlive: true, scheduling: 'lifo', timeout: 5000 });
 
 /**
  * Makes a request to a secure web server.
@@ -415,9 +416,21 @@ function get(input, options, cb) {
 
 module.exports = {
   Agent,
-  globalAgent,
   Server,
   createServer,
   get,
   request,
 };
+
+// make https.globalAgent overridable also under ECMAScript Modules
+ObjectDefineProperty(module.exports, 'globalAgent', {
+  __proto__: null,
+  configurable: true,
+  enumerable: true,
+  get() {
+    return globalAgent;
+  },
+  set(value) {
+    globalAgent = value;
+  },
+});

test/parallel/test-https-client-override-global-agent.mjs

@@ -0,0 +1,41 @@
+import { hasCrypto, skip, mustCall } from '../common';
+if (!hasCrypto) skip('missing crypto');
+import { readKey } from '../common/fixtures';
+import assert from 'assert';
+// to override https.globalAgent we need to use namespace import
+import * as https from 'https';
+
+// Disable strict server certificate validation by the client
+process.env.NODE_TLS_REJECT_UNAUTHORIZED = '0';
+
+const options = {
+  key: readKey('agent1-key.pem'),
+  cert: readKey('agent1-cert.pem'),
+};
+
+const server = https.Server(
+  options,
+  mustCall((req, res) => {
+    res.writeHead(200);
+    res.end('Hello, World!');
+  })
+);
+
+server.listen(
+  0,
+  mustCall(() => {
+    const agent = new https.Agent();
+    const name = agent.getName({ port: server.address().port });
+    https.globalAgent = agent;
+
+    makeRequest();
+    assert(name in agent.sockets); // Agent has indeed been used
+  })
+);
+
+function makeRequest() {
+  const req = https.get({
+    port: server.address().port,
+  });
+  req.on('close', () => server.close());
+}