Work around CORS issues with jsdom in auth/hub emulators. (#3224)

* Work around CORS issues with jsdom in auth/hub emulators.

* Update CHANGELOG.md

CHANGELOG.md

@@ -1,2 +1,3 @@
 - Fixes an issue where `ext:dev:init` failed when Typescript was chosen.
 - Add support for reading/writing mfaInfo field in Auth Emulator (#3173).
+- Work around CORS issues with jsdom in Auth Emulator and Emulator Hub (#3224).

package.json

@@ -92,6 +92,7 @@
     "cli-table": "^0.3.1",
     "commander": "^4.0.1",
     "configstore": "^5.0.1",
+    "cors": "^2.8.5",
     "cross-env": "^5.1.3",
     "cross-spawn": "^7.0.1",
     "csv-streamify": "^3.0.4",
@@ -146,6 +147,7 @@
     "@types/cli-color": "^0.3.29",
     "@types/cli-table": "^0.3.0",
     "@types/configstore": "^4.0.0",
+    "@types/cors": "^2.8.10",
     "@types/cross-spawn": "^6.0.1",
     "@types/dotenv": "^6.1.0",
     "@types/express": "^4.17.0",

src/emulator/auth/server.ts

@@ -1,3 +1,4 @@
+import * as cors from "cors";
 import * as express from "express";
 import * as exegesisExpress from "exegesis-express";
 import { ValidationError } from "exegesis/lib/errors";
@@ -118,20 +119,9 @@ export async function createApp(
 ): Promise<express.Express> {
   const app = express();
   app.set("json spaces", 2);
-
-  // Allow all origins and headers for CORS requests to Auth Emulator.
-  // This is safe since Auth Emulator does not use cookies.
-  app.use((req, res, next) => {
-    res.set("Access-Control-Allow-Origin", "*");
-    res.set("Access-Control-Allow-Headers", "*");
-    res.set("Access-Control-Allow-Methods", "GET, HEAD, POST, PUT, DELETE, OPTIONS, PATCH");
-    if (req.method === "OPTIONS") {
-      // This is a CORS preflight request. Just handle it.
-      res.end();
-    } else {
-      next();
-    }
-  });
+  // Enable CORS for all APIs, all origins (reflected), and all headers (reflected).
+  // This is similar to production behavior. Safe since all APIs are cookieless.
+  app.use(cors({ origin: true }));
 
   app.get("/", (req, res) => {
     return res.json({

src/emulator/hub.ts

@@ -1,3 +1,4 @@
+import * as cors from "cors";
 import * as express from "express";
 import * as os from "os";
 import * as fs from "fs";
@@ -69,6 +70,9 @@ export class EmulatorHub implements EmulatorInstance {
 
   constructor(private args: EmulatorHubArgs) {
     this.hub = express();
+    // Enable CORS for all APIs, all origins (reflected), and all headers (reflected).
+    // Safe since all Hub APIs are cookieless.
+    this.hub.use(cors({ origin: true }));
     this.hub.use(bodyParser.json());
 
     this.hub.get("/", (req, res) => {

src/test/emulators/auth/rest.spec.ts

@@ -12,6 +12,26 @@ describeAuthEmulator("REST API mapping", ({ authApi }) => {
       });
   });
 
+  it("should allow cross-origin requests", async () => {
+    await authApi()
+      .options("/")
+      .set("Origin", "example.com")
+      .set("Access-Control-Request-Headers", "Authorization,X-Client-Version,X-Whatever-Header")
+      .then((res) => {
+        expectStatusCode(204, res);
+
+        // Some clients (including older browsers and jsdom) won't accept '*' as a
+        // wildcard, so we need to reflect Origin and Access-Control-Request-Headers.
+        // https://github.com/firebase/firebase-tools/issues/3200
+        expect(res.header["access-control-allow-origin"]).to.eql("example.com");
+        expect((res.header["access-control-allow-headers"] as string).split(",")).to.have.members([
+          "Authorization",
+          "X-Client-Version",
+          "X-Whatever-Header",
+        ]);
+      });
+  });
+
   it("should handle integer values for enums", async () => {
     // Proto integer value for "EMAIL_SIGNIN". Android client SDK sends this.
     const requestType = 6;
@@ -67,6 +87,7 @@ describeAuthEmulator("authentication", ({ authApi }) => {
         expect(res.body.error).to.have.property("status").equal("PERMISSION_DENIED");
       });
   });
+
   it("should ignore non-Bearer Authorization headers", async () => {
     await authApi()
       .post("/identitytoolkit.googleapis.com/v1/accounts:signUp")