Add a toJSON() function to auth-exp (#3926)

* Add toJSON to auth-exp

* Splitting

* Formatting

Author: sam-gc

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

@@ -454,4 +454,22 @@ describe('core/auth/auth_impl useEmulator', () => {
       expect(emulatorEndpoint.calls.length).to.eq(1);
     });
   });
+
+  context('toJSON', () => {
+    it('works when theres no current user', () => {
+      expect(JSON.stringify(auth)).to.eq(
+        '{"apiKey":"test-api-key","authDomain":"localhost","appName":"test-app"}'
+      );
+    });
+
+    it('also stringifies the current user', () => {
+      auth.currentUser = ({
+        toJSON: (): object => ({ foo: 'bar' })
+      } as unknown) as User;
+      expect(JSON.stringify(auth)).to.eq(
+        '{"apiKey":"test-api-key","authDomain":"localhost",' +
+          '"appName":"test-app","currentUser":{"foo":"bar"}}'
+      );
+    });
+  });
 });

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

@@ -247,6 +247,15 @@ export class AuthImpl implements Auth, _FirebaseService {
     );
   }
 
+  toJSON(): object {
+    return {
+      apiKey: this.config.apiKey,
+      authDomain: this.config.authDomain,
+      appName: this.name,
+      currentUser: this._currentUser?.toJSON()
+    };
+  }
+
   async _setRedirectUser(
     user: User | null,
     popupRedirectResolver?: externs.PopupRedirectResolver