Add assertion for emulator url scheme in auth (firebase#3942)

* Add assertion for emulator scheme

* Formatting

* PR feedback

Author: sam-gc

packages-exp/auth-exp/src/core/auth/auth_impl.test.ts

@@ -489,6 +489,22 @@ describe('core/auth/auth_impl useEmulator', () => {
       expect(normalEndpoint.calls.length).to.eq(0);
       expect(emulatorEndpoint.calls.length).to.eq(1);
     });
+
+    it('checks the scheme properly', () => {
+      expect(() => auth.useEmulator('http://localhost:2020')).not.to.throw;
+      delete auth.config.emulator;
+      expect(() => auth.useEmulator('https://localhost:2020')).not.to.throw;
+      delete auth.config.emulator;
+      expect(() => auth.useEmulator('ssh://localhost:2020')).to.throw(
+        FirebaseError,
+        'auth/invalid-emulator-scheme'
+      );
+      delete auth.config.emulator;
+      expect(() => auth.useEmulator('localhost:2020')).to.throw(
+        FirebaseError,
+        'auth/invalid-emulator-scheme'
+      );
+    });
   });
 
   context('toJSON', () => {

packages-exp/auth-exp/src/core/auth/auth_impl.ts

@@ -203,6 +203,10 @@ export class AuthImpl implements Auth, _FirebaseService {
       appName: this.name
     });
 
+    assert(/^https?:\/\//.test(url), AuthErrorCode.INVALID_EMULATOR_SCHEME, {
+      appName: this.name
+    });
+
     this.config.emulator = { url };
     this.settings.appVerificationDisabledForTesting = true;
   }

packages-exp/auth-exp/src/core/errors.ts

@@ -56,6 +56,7 @@ export const enum AuthErrorCode {
   INVALID_CUSTOM_TOKEN = 'invalid-custom-token',
   INVALID_DYNAMIC_LINK_DOMAIN = 'invalid-dynamic-link-domain',
   INVALID_EMAIL = 'invalid-email',
+  INVALID_EMULATOR_SCHEME = 'invalid-emulator-scheme',
   INVALID_IDP_RESPONSE = 'invalid-credential',
   INVALID_MESSAGE_PAYLOAD = 'invalid-message-payload',
   INVALID_MFA_SESSION = 'invalid-multi-factor-session',
@@ -189,6 +190,8 @@ const ERRORS: ErrorMap<AuthErrorCode> = {
   [AuthErrorCode.INVALID_DYNAMIC_LINK_DOMAIN]:
     'The provided dynamic link domain is not configured or authorized for the current project.',
   [AuthErrorCode.INVALID_EMAIL]: 'The email address is badly formatted.',
+  [AuthErrorCode.INVALID_EMULATOR_SCHEME]:
+    'Emulator URL must start with a valid scheme (http:// or https://).',
   [AuthErrorCode.INVALID_API_KEY]:
     'Your API key is invalid, please check you have copied it correctly.',
   [AuthErrorCode.INVALID_CERT_HASH]: