fix(@aws-amplify/auth): No Auth module registered in Amplify

packages/core/__tests__/Credentials-test.ts

@@ -26,6 +26,30 @@ const cacheClass = {
 };
 
 describe('Credentials test', () => {
+	describe('.Auth', () => {
+		it('should be undefined by default', async () => {
+			const credentials = new Credentials(null);
+
+			expect(credentials.Auth).toBeUndefined();
+
+			expect(credentials.get()).rejects.toMatchInlineSnapshot(
+				`"No Auth module registered in Amplify"`
+			);
+		});
+
+		it('should be Amplify.Auth if configured through Amplify', () => {
+			const credentials = new Credentials(null);
+
+			Amplify.register(authClass);
+			Amplify.register(credentials);
+
+			Amplify.configure({});
+
+			expect(credentials.Auth).toBe(authClass);
+			expect(credentials.get()).resolves.toBe('cred');
+		});
+	});
+
 	describe('configure test', () => {
 		test('happy case', () => {
 			const config = {

packages/core/src/Credentials.ts

@@ -33,8 +33,8 @@ export class CredentialsClass {
 	private _identityId;
 	private _nextCredentialsRefresh: Number;
 
-	// `Amplify.Auth` will either be `Auth` or `null` depending on if Auth was imported
-	Auth = Amplify.Auth;
+	// Allow `Auth` to be injected for SSR, but Auth isn't a required dependency for Credentials
+	Auth = undefined;
 
 	constructor(config) {
 		this.configure(config);
@@ -105,8 +105,11 @@ export class CredentialsClass {
 		logger.debug('need to get a new credential or refresh the existing one');
 
 		// Some use-cases don't require Auth for signing in, but use Credentials for guest users (e.g. Analytics)
-		if (this.Auth && typeof this.Auth.currentUserCredentials === 'function') {
-			return this.Auth.currentUserCredentials();
+		// Prefer locally scoped `Auth`, but fallback to registered `Amplify.Auth` global otherwise.
+		const { Auth = Amplify.Auth } = this;
+
+		if (Auth && typeof Auth.currentUserCredentials === 'function') {
+			return Auth.currentUserCredentials();
 		} else {
 			return Promise.reject('No Auth module registered in Amplify');
 		}