How do I validate and secure deep links in my MvvmCross application

Configuration and Setup

1. Deep Link Configuration:
- Android: In the `AndroidManifest.xml`, define intent filters for activities that should handle deep links. Use `` tags to specify the scheme, host, and path. Ensure the activity is exported by setting `android:exported="true"`[3].
- iOS: In the `Info.plist`, add a custom URL scheme under `CFBundleURLTypes`. This will allow your app to handle specific URLs[8].

2. MvvmCross Routing Plugin:
- Use the MvvmCross Routing Plugin to handle deep links. This plugin supports URL-based navigation and allows multiple URIs per ViewModel[2][4].
- Define routing attributes on ViewModels using assembly attributes, specifying the URI pattern and parameters[2][4].

Handling Deep Links

1. Android Handling:
- Override `OnNewIntent` in the activity that handles deep links. This method is called when a new intent is delivered to the activity, allowing you to handle deep links when the app is already running[2][4].
- Use the MvvmCross Routing Service to navigate to the appropriate ViewModel based on the deep link URI[2].

2. iOS Handling:
- Override `OpenUrl` in the `AppDelegate.cs`. This method is called when the app is opened from a deep link. Use this to navigate to the appropriate ViewModel using the MvvmCross Routing Service[1][2].

Validation and Security

1. Input Validation:
- Always validate the parameters passed through deep links to prevent unauthorized access or data manipulation. Use regular expressions or other validation methods to ensure parameters match expected formats[3].

2. Secure Data Handling:
- Ensure that sensitive data passed through deep links is encrypted or handled securely. Avoid passing sensitive information directly in URLs; instead, use tokens or identifiers that can be resolved securely within the app[8].

3. Testing Deep Links:
- Use tools like Android Debug Bridge (ADB) for Android or iOS-specific testing frameworks to simulate deep link scenarios. This helps verify that deep links navigate to the correct sections of the app and handle parameters correctly[6][7].

4. Security Audits:
- Regularly perform security audits to ensure that deep links do not introduce vulnerabilities. Check for potential issues like data exposure or unauthorized access paths[3].

Example Code

Here's an example of how to define a routing attribute for a ViewModel in MvvmCross:

csharp
[assembly: MvxRouting(typeof(ViewModelA), @"mvx://test/\?id=(?[A-Z0-9]{32})$")]
namespace *.ViewModels
{
    public class ViewModelA : MvxViewModel
    {
        public void Init(string id)
        {
            // Handle the id parameter here
        }
    }
}

And here's how you might handle deep links in iOS:

csharp
public class AppDelegate : MvxApplicationDelegate
{
    public override bool OpenUrl(UIApplication application, NSUrl url, string sourceApplication, NSObject annotation)
    {
        // Use the MvvmCross Routing Service to navigate based on the URL
        var routingService = Mvx.Resolve();
        routingService.RouteAsync(url.AbsoluteString);
        return true;
    }
}

By following these steps and ensuring proper validation and security measures, you can effectively validate and secure deep links in your MvvmCross application.