Fix uncaught exceptions in acquireTokenSilent (#7073)

A recent change to optimize parallel iframed calls resulted in a
regression that logged an uncaught exception to the console in the event
that a single iframed call was made and failed. This happened because
the stored promise rejected and didn't have a catch handler registered
because there is not a parallel call dependent on this promise.

This PR resolves this issue by ensuring that the stored promise never
rejects but rather resolves with a true/false indicating whether the
call succeeded or failed.

Fixes #7052

change/@azure-msal-browser-94058809-8f02-4078-bdc6-02ff59c54ae3.json

@@ -0,0 +1,7 @@
+{
+  "type": "patch",
+  "comment": "Fix uncaught exceptions in acquireTokenSilent #7073",
+  "packageName": "@azure/msal-browser",
+  "email": "[email protected]",
+  "dependentChangeType": "patch"
+}

lib/msal-browser/src/controllers/StandardController.ts

@@ -158,7 +158,7 @@ export class StandardController implements IController {
     >;
 
     // Active Iframe request
-    private activeIframeRequest: [Promise<void>, string] | undefined;
+    private activeIframeRequest: [Promise<boolean>, string] | undefined;
 
     private ssoSilentMeasurement?: InProgressPerformanceEvent;
     private acquireTokenByCodeAsyncMeasurement?: InProgressPerformanceEvent;
@@ -2039,13 +2039,11 @@ export class StandardController implements IController {
 
             if (shouldTryToResolveSilently) {
                 if (!this.activeIframeRequest) {
-                    let _resolve: () => void,
-                        _reject: (reason?: AuthError | Error) => void;
+                    let _resolve: (result: boolean) => void;
                     // Always set the active request tracker immediately after checking it to prevent races
                     this.activeIframeRequest = [
-                        new Promise((resolve, reject) => {
+                        new Promise((resolve) => {
                             _resolve = resolve;
-                            _reject = reject;
                         }),
                         silentRequest.correlationId,
                     ];
@@ -2061,11 +2059,11 @@ export class StandardController implements IController {
                         silentRequest.correlationId
                     )(silentRequest)
                         .then((iframeResult) => {
-                            _resolve();
+                            _resolve(true);
                             return iframeResult;
                         })
                         .catch((e) => {
-                            _reject(e);
+                            _resolve(false);
                             throw e;
                         })
                         .finally(() => {
@@ -2087,20 +2085,11 @@ export class StandardController implements IController {
                         awaitIframeCorrelationId: activeCorrelationId,
                     });
 
-                    // Await for errors first so we can distinguish errors thrown by activePromise versus errors thrown by .then below
-                    await activePromise.catch(() => {
-                        awaitConcurrentIframeMeasure.end({
-                            success: false,
-                        });
-                        this.logger.info(
-                            `Iframe request with correlationId: ${activeCorrelationId} failed. Interaction is required.`
-                        );
-                        // If previous iframe request failed, it's unlikely to succeed this time. Throw original error.
-                        throw refreshTokenError;
+                    const activePromiseResult = await activePromise;
+                    awaitConcurrentIframeMeasure.end({
+                        success: activePromiseResult,
                     });
-
-                    return activePromise.then(() => {
-                        awaitConcurrentIframeMeasure.end({ success: true });
+                    if (activePromiseResult) {
                         this.logger.verbose(
                             `Parallel iframe request with correlationId: ${activeCorrelationId} succeeded. Retrying cache and/or RT redemption`,
                             silentRequest.correlationId
@@ -2110,7 +2099,13 @@ export class StandardController implements IController {
                             silentRequest,
                             cacheLookupPolicy
                         );
-                    });
+                    } else {
+                        this.logger.info(
+                            `Iframe request with correlationId: ${activeCorrelationId} failed. Interaction is required.`
+                        );
+                        // If previous iframe request failed, it's unlikely to succeed this time. Throw original error.
+                        throw refreshTokenError;
+                    }
                 } else {
                     // Cache policy set to skip and another iframe request is already in progress
                     this.logger.warning(

lib/msal-browser/test/app/PublicClientApplication.spec.ts

@@ -4817,6 +4817,43 @@ describe("PublicClientApplication.ts Class Unit Tests", () => {
                 });
         });
 
+        it("throws iframe error if iframe renewal throws", (done) => {
+            const testAccount: AccountInfo = {
+                homeAccountId: TEST_DATA_CLIENT_INFO.TEST_HOME_ACCOUNT_ID,
+                localAccountId: TEST_DATA_CLIENT_INFO.TEST_UID,
+                environment: "login.windows.net",
+                tenantId: "testTenantId",
+                username: "[email protected]",
+            };
+
+            jest.spyOn(
+                RefreshTokenClient.prototype,
+                "acquireTokenByRefreshToken"
+            ).mockRejectedValue(
+                createInteractionRequiredAuthError(
+                    InteractionRequiredAuthErrorCodes.refreshTokenExpired
+                )
+            );
+
+            const testIframeError = new InteractionRequiredAuthError(
+                "interaction_required",
+                "interaction is required"
+            );
+
+            jest.spyOn(
+                SilentIframeClient.prototype,
+                "acquireToken"
+            ).mockRejectedValue(testIframeError);
+
+            pca.acquireTokenSilent({
+                scopes: ["Scope1"],
+                account: testAccount,
+            }).catch((e) => {
+                expect(e).toEqual(testIframeError);
+                done();
+            });
+        });
+
         it("Falls back to silent handler if thrown error is a refresh token expired error", async () => {
             const invalidGrantError: ServerError = new ServerError(
                 "invalid_grant",