Add debug feature to always enable cors for emulated v2 https functions

src/common/debug.ts

@@ -25,6 +25,7 @@ const debugMode = process.env.FIREBASE_DEBUG_MODE === 'true';
 
 interface DebugFeatures {
   skipTokenVerification?: boolean;
+  enableCors?: boolean;
 }
 
 function loadDebugFeatures(): DebugFeatures {

src/v2/providers/https.ts

@@ -34,6 +34,7 @@ import {
 import { ManifestEndpoint } from '../../runtime/manifest';
 import * as options from '../options';
 import { GlobalOptions, SupportedRegion } from '../options';
+import { isDebugFeatureEnabled } from '../../common/debug';
 
 export { Request, CallableRequest, FunctionsErrorCode, HttpsError };
 
@@ -89,12 +90,13 @@ export function onRequest(
     opts = optsOrHandler as HttpsOptions;
   }
 
-  if ('cors' in opts) {
+  if (isDebugFeatureEnabled('enableCors') || 'cors' in opts) {
+    const corsOrigin = isDebugFeatureEnabled('enableCors') ? true : opts.cors;
     const userProvidedHandler = handler;
     handler = (req: Request, res: express.Response): void | Promise<void> => {
       return new Promise((resolve) => {
         res.on('finish', resolve);
-        cors({ origin: opts.cors })(req, res, () => {
+        cors({ origin: corsOrigin })(req, res, () => {
           resolve(userProvidedHandler(req, res));
         });
       });
@@ -179,7 +181,11 @@ export function onCall<T = any, Return = any | Promise<any>>(
     opts = optsOrHandler as HttpsOptions;
   }
 
-  const origin = 'cors' in opts ? opts.cors : true;
+  const origin = isDebugFeatureEnabled('enableCors')
+    ? true
+    : 'cors' in opts
+    ? opts.cors
+    : true;
 
   // onCallHandler sniffs the function length to determine which API to present.
   // fix the length to prevent api versions from being mismatched.