Trinsic Flutter UI Library

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The Trinsic Flutter UI Library provides ways to launch verification sessions directly from your Flutter application requiring very little code.

This library must be paired with a api library as part of a full integration.

Currently, only iOS and Android are supported.

Installation

Simply add this library to your Flutter project:

flutter pub add trinsic_flutter_ui

Then import it in your code:

import 'package:trinsic_flutter_ui/trinsic_flutter_ui.dart';

Setup

Choose a Custom Scheme

This library makes use of Android Custom Tabs on Android and ASWebAuthenticationSession on iOS.

Therefore, you must register a custom scheme against your app on both Android and iOS in order for the library to be able to capture the results of a session.

This custom scheme can be the same between iOS and Android, but should be globally unique to your organization and application.

An example of a good custom scheme might be acme-corp-shopping-app-trinsic.

iOS

Minimum version

The iOS SDK supports iOS from version 13.4 for securely launching authentication sessions. Make sure to upgrade your Podfile dependency and XCode minimum target.

Configure your iOS Podfile to use static libraries

If you're not already using static libraries, add the following line to your podfile to be able to use our Swift module:

use_frameworks! :linkage => :static

Add the scheme to your app's URLs

Select your app's target and on the info tab in XCode add the scheme you selected.

Android

Minimum SDK Version & Default taskAffinity

Note

Although increasing your app's minimum SDK version to 28 or higher is technically optional, it is the only way to remove the Flutter-generated android:taskAffinity="" property without reducing your application's resistance to StrandHogg.

It is worth considering that the taskAffinity mitigation is only partial -- the only way to fully protect your app from this vulnerability is to set a minimum SDK version of 28 or higher, as Google recommends.

Finally, note that this library has no bearing on your application's security -- this vulnerability is present regardless of whether this library is in use or not, as it is inherent to Android. It is only relevant to this library because it cannot function if your app specifies an empty taskAffinity.

You will need to make two changes to the Android scaffolding which Flutter auto-generated for your app.

  1. In your app's AndroidManifest.xml, remove the android:taskAffinity="" directive on your main activity's declaration
    1. The library cannot function if your main activity has an empty task affinity
    2. If you wish to use a custom (non-empty) task affinity, refer to our Android SDK documentation to set this up
  2. Modify your app's build.gradle[.kts] to increase the minSdk directive to at least 28
    1. This is necessary for the security of your application (explained below)

These changes are necessary to A) ensure library functionality and B) do so in a way that maintains application security.

Flutter automatically adds taskAffinity="" to your app's manifest in order to mitigate a security issue; however, this directive breaks libraries which use Android Custom Tabs in the way we do, as it changes Android's task management logic in an incompatible way.

This security issue is entirely mitigated on Android SDK versions 28 and up. Therefore, both changes (removing the empty task affinity and increasing the minimum android SDK version of your app) are necessary to ensure functionality without reducing security.

Register Library in AndroidManifest.xml

Place the following snippet in your app's AndroidManifest.xml, replacing [YOURCUSTOMSCHEME] with the scheme you chose in step 1

<activity
    android:name="id.trinsic.android.ui.CallbackActivity"
    android:exported="true">
    <intent-filter android:label="trinsic">
        <action android:name="android.intent.action.VIEW" />
        <category android:name="android.intent.category.DEFAULT" />
        <category android:name="android.intent.category.BROWSABLE" />

        <data android:scheme="[YOURCUSTOMSCHEME]" />
    </intent-filter>
</activity>

Usage

Once your backend has created a Session and passed the launchUrl to your app, simply invoke the plugin, passing a redirect URL containing the custom scheme you registered above.

The redirect URL can have any path, as long as its scheme is correct. EG, both acme-corp-shopping-app-trinsic:///callback and acme-corp-shopping-app-trinsic:///callback-2 are valid redirect URLs.

License

MIT

Libraries

trinsic_flutter_method_channel
trinsic_flutter_platform_interface
trinsic_flutter_ui