[Bug]: Android does not inject the Capacitor bridge after navigating to an allowNavigation URL #8661

Capacitor Version

💊 Capacitor Doctor 💊

Latest Dependencies:

@capacitor/cli: 8.5.3
@capacitor/core: 8.5.3
@capacitor/android: 8.5.3
@capacitor/ios: 8.5.3

Installed Dependencies:

@capacitor/cli: 8.5.3
@capacitor/core: 8.5.3
@capacitor/android: 8.5.3
@capacitor/ios: 8.5.3

[success] iOS looking great! 👌
[success] Android looking great! 👌

Other API Details

Platforms Affected

• iOS
• Android
• Web

Current Behavior

On Android, the app starts on the local origin (https://localhost) and then navigates with window.location to a remote URL listed in server.allowNavigation (for example https://client.example.com).

allowNavigation keeps the navigation inside the WebView, but native plugins stop working on the remote page. Calls fail with UNIMPLEMENTED / "plugin is not implemented on android". window.Capacitor.PluginHeaders is empty on the new origin.

Cause: Bridge.loadWebView() registers the bridge with WebViewCompat.addDocumentStartJavaScript only for the appUrl origin:

WebViewCompat.addDocumentStartJavaScript(webView, injector.getScriptString(), Collections.singleton(allowedOrigin));

allowedOrigin is derived from appUrl (https://localhost). The allowNavigation origins are already collected in allowedOriginRules, but that set is not passed to addDocumentStartJavaScript.

iOS does not have this problem. WKUserScript is injected at document start on every main-frame load, with no origin filter, so plugins keep working after the same redirect.

This is still the case in the 8.5.3 tag, and also in 9.0.0-alpha.8:
https://github.com/ionic-team/capacitor/blob/8.5.3/android/capacitor/src/main/java/com/getcapacitor/Bridge.java

Expected Behavior

After navigating to a URL allowed by server.allowNavigation, Android should keep the native bridge, same as iOS.

addDocumentStartJavaScript should receive allowedOriginRules (local origin, server.url when set, and allowNavigation origins), not only the appUrl origin. Plugins should keep working on the remote page without an app-level patch of Bridge.java.

Project Reproduction

https://github.com/Dylancyclone/capacitor-android-redirect

Additional Information

Same bug as #7454, still open. The reproduction repo linked above is the one from that issue. The one-line fix is already in #8429 (rebased from #7571) and has had no maintainer review. #7571 was closed for backlog rebase, not because the change was rejected.

Please land #8429, or apply the same change on main:

•    WebViewCompat.addDocumentStartJavaScript(webView, injector.getScriptString(), Collections.singleton(allowedOrigin));
  

•    WebViewCompat.addDocumentStartJavaScript(webView, injector.getScriptString(), allowedOriginRules);
  

Reproduced on 8.5.3. The same line is still present in 9.0.0-alpha.8. Apps currently have to patch @capacitor/android themselves to get iOS parity.