PopupBridge iOS

PopupBridge is an iOS library that allows WKWebViews to open popup windows in an ASWebAuthenticationSession browser and send data back to the parent page in the WKWebView.

PopupBridge is also available for Android.

See the Frequently Asked Questions to learn more about PopupBridge. See Using PayPal in a WebView to use PopupBridge with PayPal.

Requirements

• iOS 14.0+
• Xcode 15.0+
• Swift 5.9+, or Objective-C

Installation

CocoaPods

To integrate using CocoaPods, add the following line to your Podfile:

pod 'PopupBridge'

Carthage

To integrate using Carthage, add github "braintree/popup-bridge-ios" to your Cartfile, and add the frameworks to your project.

Swift Package Manager

To integrate using Swift Package Manager, select File > Swift Packages > Add Package Dependency and enter https://github.com/braintree/popup-bridge-ios as the repository URL. Tick the checkbox for PopupBridge.

If you look at your app target, you will see that PopupBridge is automatically linked as a framework to your app (see General > Frameworks, Libraries, and Embedded Content).

Sample App

To run the sample app, clone the repo, open PopupBridge.xcworkspace and run the Demo app target.

Quick Start

1. Integrate PopupBridge with your WKWebView:

   class ViewController: UIViewController {
   
       var webView: WKWebView = WKWebView(frame: CGRect(x: 0, y: 0, width: 300, height: 700))
       var popupBridge: POPPopupBridge?
   
       override func viewDidLoad() {
           super.viewDidLoad()
   
           view.addSubview(webView)
   
           popupBridge = POPPopupBridge(webView: webView)
   
           // Replace http://localhost:3099/ with the webpage you want to open in the webview
           let url = URL(string: "http://localhost:3099/")!
           webView.load(URLRequest(url: url))
       }
   }

2. Use PopupBridge from the web page by writing some JavaScript:

   var url = 'http://localhost:3099/popup'; // or whatever the page is that you want to open in a popup
   
   if (window.popupBridge) {
     // Open the popup in a browser, and give it the deep link back to the app
     popupBridge.open(url + '?popupBridgeReturnUrlPrefix=' + popupBridge.getReturnUrlPrefix());
   
     // Optional: define a callback to process results of interaction with the popup
     popupBridge.onComplete = function (err, payload) {
       if (err) {
         console.error('PopupBridge onComplete Error:', err);
       } else if (!err && !payload) {
         console.log('User closed popup.');
       } else {
         alert('Your favorite color is ' + payload.queryItems.color);
       }
     };
   } else {
     var popup = window.open(url);
   
     window.addEventListener('message', function (event) {
       var color = JSON.parse(event.data).color;
   
       if (color) {
         popup.close();
         alert('Your favorite color is ' + color);
       }
     });
   }

3. Redirect back to the app inside of the popup:

   <h1>What is your favorite color?</h1>
   
   <a href="#red" data-color="red">Red</a>
   <a href="#green" data-color="green">Green</a>
   <a href="#blue" data-color="blue">Blue</a>
   
   <script src="https://github.com/braintree/popup-bridge-ios/raw/main/jquery.js"></script>
   <script>
   $('a').on('click', function (event) {
     var color = $(this).data('color');
   
     if (location.search.indexOf('popupBridgeReturnUrlPrefix') !== -1) {
       var prefix = location.search.split('popupBridgeReturnUrlPrefix=')[1];
       // Open the deep link back to the app, and send some data
       location.href = prefix + '?color=' + color;
     } else {
       window.opener.postMessage(JSON.stringify({ color: color }), '*');
     }
   });
   </script>

Frequently Asked Questions

Why use PopupBridge?

WKWebView can open popups through its WKUIDelegate, which can be implemented to present the popup in a new WKWebView.

However, WKWebViews do not display an address bar or an HTTPS lock icon. If the popup receives sensitive user information (e.g. login credentials), users must implicitly trust that the web page is not redirecting them to a malicious spoofed page that may steal their information. PopupBridge solves this by using an ASWebAuthenticationSession.

What are some use cases for using PopupBridge?

• Apps with WebViews that need to open a popup
• When a popup window needs to to send data from the popup back to the WKWebView
• When the popup window needs to display the HTTPS lock icon to increase user trust
• Apps that use OAuth

How does it work?

• PopupBridge attaches to a WKWebView by injecting a user script to the page
  • This exposes a JavaScript interface (via window.popupBridge) for the web page to interact with the iOS code
• The web page detects whether the page has access to window.popupBridge; if so, it creates a ASWebAuthenticationSession to open the popup URL
  • The web page can also use popupBridge.onComplete as a callback
• If the user taps the Cancel button on the ASWebAuthenticationSession, popupBridge.onComplete gets called with the error and payload as null

Who built PopupBridge?

We are engineers who work on the Developer Experience team at Braintree.

Why did Braintree build PopupBridge?

Short answer: to accept PayPal as a payment option when mobile apps are using a WebView to power the checkout process.

PayPal authentication occurs in a popup window. However, this causes issues with Braintree merchants who use a web page to power payments within their apps: they can't accept PayPal because WebViews cannot open popups and return the PayPal payment authorization data to the parent checkout page.

PopupBridge solves this problem by allowing braintree-web or PayPal's Checkout.js to open the PayPal popup from a secure mini-browser.

Using PayPal in a WebView

WebView-based checkout flows can accept PayPal with PopupBridge and the Braintree JS SDK or PayPal's Checkout.js. For the authentication flow, PayPal requires a popup window—which can be simulated with PopupBridge.

Setup

1. Create a web-based checkout that accepts PayPal using Checkout.js or the Braintree JS SDK
2. Create a native mobile app that opens the checkout in a WKWebView (See the quick start instructions)
3. Integrate the PopupBridge library
4. Collect device data
   • To help detect fraudulent activity, collect device data before performing PayPal transactions. This is similar to collecting device data with our native iOS SDK with a few differences:
     1. Rather than importing the entire data collector, you can add just PayPalDataCollector to your app: pod 'Braintree/PayPalDataCollector'
     2. Implement methods in your native app depending on whether you are doing one-time payments or vaulted payments. See the iOS code snippets for PayPal + PopupBridge
5. Profit!

Versions

This SDK abides by our Client SDK Deprecation Policy. For more information on the potential statuses of an SDK check our developer docs.

Author

Braintree, code@getbraintree.com

License

PopupBridge is available under the MIT license. See the LICENSE file for more info.