Troubleshooting URI Redirect Issues with WebAuthenticatorCallbackActivity in Android

Implementing OAuth 2.0 flows in Android applications often involves using a WebAuthenticatorCallbackActivity to handle the redirect URI after the user has authenticated with the authorization server. However, developers sometimes face frustrating issues where the callback activity is not invoked as expected, even when the redirect URI seems correct. This article will delve into common reasons and solutions for this problem, using a real-world scenario as an example.

The Scenario: OAuth Callback Fails

Consider an Android app using Xamarin.Android for development, attempting to integrate with OneDrive via OAuth. The developer has set up an activity called AuthOneDriveCallbackActivity to handle the callback from the OneDrive authorization server. This activity is decorated with attributes to define its intent filters.

[Activity(Label = "AuthOneDriveCallbackActivity", NoHistory = true, Exported = true, LaunchMode = global::Android.Content.PM.LaunchMode.SingleTop)]
[IntentFilter(
new[] { Intent.ActionView },
Categories = new[] { Intent.CategoryDefault, Intent.CategoryBrowsable },
DataScheme = "https",
DataHost = "login.live.com",
DataPath = "/oauth20_desktop.srf"
)]
public class AuthOneDriveCallbackActivity : WebAuthenticatorCallbackActivity
{
}

The expected behavior is that after the user authenticates in the custom tab, the browser should redirect to a URL matching the defined DataScheme, DataHost, and DataPath. However, the application doesn't return to the app; instead, a blank page with the relevant URL is displayed.

Common Causes and Solutions

Here's a breakdown of potential causes and actionable steps to troubleshoot these frustrating scenarios:

1. Manifest Configuration Errors:

   • android:exported attribute: Ensure the android:exported attribute is set to true in the Activity declaration in the AndroidManifest.xml file. Otherwise, the system cannot launch the activity.

   <activity android:name=".AuthOneDriveCallbackActivity" android:label="AuthOneDriveCallbackActivity" android:exported="true">
     <intent-filter>
       <action android:name="android.intent.action.VIEW" />
       <category android:name="android.intent.category.DEFAULT" />
       <category android:name="android.intent.category.BROWSABLE" />
       <data android:scheme="https" android:host="login.live.com" android:path="/oauth20_desktop.srf" />
     </intent-filter>
   </activity>
   

   Copy
   • Data Path Prefix vs. Exact Match: Pay close attention to whether your DataPath should be treated as a prefix or an exact match. If you intend to match any path starting with /oauth20_desktop.srf, use DataPathPrefix instead of DataPath.

2. Scheme Handling Conflicts:

   • Multiple Activities Handling the Same Scheme: If other activities or apps on the device are also configured to handle the same scheme (https), the system might present a disambiguation dialog. Ensure that the intent filters are unique enough to avoid conflicts.

3. Custom Tabs and Intent Resolution:

   • Browser Selection: Ensure a browser that supports custom tabs is correctly installed and functioning. Issues with the browser itself can sometimes interfere with intent resolution. You can try specifying a preferred browser for testing purposes.
   • Intent Flags: When constructing the authorization URL, ensure you are using the appropriate intent flags to prevent the browser from creating a new task (which might not return to your app correctly).

4. Redirect URI Mismatch:

   • URL Encoding: Double-check that the redirect URI you specify in your OAuth request exactly matches the one configured in your application's manifest. URL encoding issues are a common culprit. For instance, %20 (space) or other encoded characters in the URI could lead to a mismatch.

   • Trailing Slash: Be mindful of trailing slashes (/) in your DataPath. A mismatch can occur if your redirect URI from the server contains a trailing slash, but your DataPath declaration doesn't or vice versa.

5. Asynchronous Operations and UI Thread Issues:

   • The Skipped Frames is indicative of performance bottle necks. It's crucial to avoid heavy computations or network operations directly on the main thread. Consider using async and await to perform operations asynchronously. If you suspect the UI thread is overloaded, use tools like the Android Profiler to identify performance bottlenecks.

6. Debugging with ADB (Android Debug Bridge):

   • Intent Resolution: Use the ADB command to manually trigger the intent and see which activity is resolved. This helps determine if the issue lies in the intent filter matching or something else.

   adb shell am start -a android.intent.action.VIEW \
   -c android.intent.category.DEFAULT \
   -c android.intent.category.BROWSABLE \
   -d "YOUR_REDIRECT_URI"
   

   Replace YOUR_REDIRECT_URI with the actual redirect URI you expect.

Analyzing Logs

The provided logs are filled with information, but a few key clues can be identified:

1. TransactionTooLargeException The logs indicate remote TransactionTooLargeException. This suggests that you might be passing a large amount of data between processes (likely the custom tab and your app). Examine the data you're sending back in the redirect URI (e.g., the authorization code). If it's excessively large, consider alternative methods for transferring data, such as using shared preferences or internal storage to store the data.

2. Segmentation fault Chrome crashes with Segmentation fault which may related with memory access violation. Check which Chrome version your device has. Consider to use another browser to make sure that it works well.

Example Code Snippet (Java)

While the original example is in Xamarin/C#, the core concepts apply to native Java Android development as well. Here's how you might define the callback activity in Java:

import android.app.Activity;
import android.content.Intent;
import android.net.Uri;
import android.os.Bundle;

@Activity(label = "AuthOneDriveCallbackActivity", exported = true, launchMode = android.content.pm.ActivityInfo.LAUNCH_SINGLE_TOP, noHistory = true)
public class AuthOneDriveCallbackActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        Intent intent = getIntent();
        Uri uri = intent.getData();

        if (uri != null) {
            // Process the URI and extract the authorization code or tokens
            String authorizationCode = uri.getQueryParameter("code");

            // TODO: Handle the successful authentication and token exchange
        } else {
            // Handle the error case
        }

        // Finish the activity
        finish();
    }
}

And the corresponding entry in AndroidManifest.xml:

<activity
    android:name=".AuthOneDriveCallbackActivity"
    android:exported="true"
    android:label="AuthOneDriveCallbackActivity"
    android:launchMode="singleTop"
    android:noHistory="true">
    <intent-filter>
        <action android:name="android.intent.action.VIEW" />

        <category android:name="android.intent.category.DEFAULT" />
        <category android:name="android.intent.category.BROWSABLE" />

        <data
            android:scheme="https"
            android:host="login.live.com"
            android:path="/oauth20_desktop.srf" />
    </intent-filter>
</activity>

Summary

Troubleshooting URI redirect issues with WebAuthenticatorCallbackActivity can be complex. A meticulous approach, systematically verifying manifest configurations, redirect URI accuracy, browser behavior, and debugging with ADB, will help pinpoint the root cause. Consider Chrome crashes, that maybe related with the Chrome's problems itself. By addressing these potential issues, developers can ensure that OAuth flows in their Android applications function smoothly.