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For our new friends:

Logto is an Auth0 alternative designed for modern apps and SaaS products. It offers both Cloud and Open-source services to help you quickly launch your identity and management (IAM) system. Enjoy authentication, authorization, and multi-tenant management all in one.

We recommend starting with a free development tenant on Logto Cloud. This allows you to explore all the features easily.

In this article, we will go through the steps to quickly build the Twilio sign-in experience (user authentication) with Flutter and Logto.

Prerequisites

  • A running Logto instance. Check out the introduction page to get started.
  • Basic knowledge of Flutter.
  • A usable Twilio account.

Create an application in Logto​

Logto is based on OpenID Connect (OIDC) authentication and OAuth 2.0 authorization. It supports federated identity management across multiple applications, commonly called Single Sign-On (SSO).

To create your Native app application, simply follow these steps:

  1. Open the Logto Console. In the "Get started" section, click the "View all" link to open the application frameworks list. Alternatively, you can navigate to Logto Console > Applications, and click the "Create application" button. Get started
  2. In the opening modal, click the "Native app" section or filter all the available "Native app" frameworks using the quick filter checkboxes on the left. Click the "Flutter" framework card to start creating your application. Frameworks
  3. Enter the application name, e.g., "Bookstore," and click "Create application".

🎉 Ta-da! You just created your first application in Logto. You'll see a congrats page which includes a detailed integration guide. Follow the guide to see what the experience will be in your application.

Integrate Logto SDK​

tip:
  • The SDK package is available on pub.dev and Logto GitHub repository.
  • The sample project is built using Flutter material. You can find it on pub.dev.
  • This SDK is compatible with Flutter applications on iOS, Android, and Web platforms. Compatibility with other platforms has not been tested.

Installation​

You can install the logto_dart_sdk package directly using the pub package manager. Run the following command under your project root:

flutter pub add logto_dart_sdk

Or add the following to your pubspec.yaml file:

dependencies:
  logto_dart_sdk: ^3.0.0

Then run:

flutter pub get

Dependency and configurations​

SDK version compatibility​

Logto SDK versionDart SDK versionDart 3.0 compatible
< 2.0.0>= 2.17.6 < 3.0.0false
>= 2.0.0 < 3.0.0>= 3.0.0true
>= 3.0.0>= 3.6.0true

flutter_secure_storage set up​

Under the hood, this SDK uses flutter_secure_storage to implement the cross-platform persistent secure token storage.

  • Keychain is used for iOS
  • AES encryption is used for Android.

Config Android version​

Set the android:minSdkVersion to >= 18 in your project's android/app/build.gradle file.

build.gradle
  android {
      ...

      defaultConfig {
          ...
          minSdkVersion 18
          ...
      }
  }

Disable auto backup on Android​

By default Android backups data on Google Drive. It can cause exception java.security.InvalidKeyException:Failed to unwrap key. To avoid this,

  1. To disable auto backup, go to your app manifest file and set the android:allowBackup and android:fullBackupContent attributes to false.

    AndroidManifest.xml
    <manifest ... >
        ...
        <application
          android:allowBackup="false"
          android:fullBackupContent="false"
          ...
        >
            ...
        </application>
    </manifest>

  2. Exclude sharedprefs from FlutterSecureStorage.

    If you need to keep the android:fullBackupContent for your app rather than disabling it, you can exclude the sharedprefs directory from the backup. See more details in the Android documentation.

    In your AndroidManifest.xml file, add the android:fullBackupContent attribute to the <application> element, as shown in the following example. This attribute points to an XML file that contains backup rules.

    AndroidManifest.xml
    <application ...
      android:fullBackupContent="@xml/backup_rules">
    </application>

    Create an XML file called @xml/backup_rules in the res/xml/ directory. In this file, add rules with the <include> and <exclude> elements. The following sample backs up all shared preferences except device.xml:

    @xml/backup_rules
    <?xml version="1.0" encoding="utf-8"?>
    <full-backup-content>
      <exclude domain="sharedpref" path="FlutterSecureStorage"/>
    </full-backup-content>

Please check flutter_secure_storage for more details.

flutter_web_auth_2 set up​

Behind the scenes, this SDK uses flutter_web_auth_2 to authenticate users with Logto. This package provides a simple way to authenticate users with Logto using the system webview or browser.

This plugin uses ASWebAuthenticationSession on iOS 12+ and macOS 10.15+, SFAuthenticationSession on iOS 11, Chrome Custom Tabs on Android and opens a new window on Web.

  • iOS: No additional setup required

  • Android: Register the callback url on Android

    In order to capture the callback url from Logto's sign-in web page, you will need to register your sign-in redirectUri to your AndroidManifest.xml file.

    AndroidManifest.xml
      <manifest>
        <application>
            <activity
              android:name="com.linusu.flutter_web_auth_2.CallbackActivity"
              android:exported="true">
              <intent-filter android:label="flutter_web_auth_2">
              <action android:name="android.intent.action.VIEW" />
              <category android:name="android.intent.category.DEFAULT" />
              <category android:name="android.intent.category.BROWSABLE" />
              <data android:scheme="YOUR_CALLBACK_URL_SCHEME_HERE" />
              </intent-filter>
            </activity>
        </application>
      </manifest>

  • Web browser: Create an endpoint to handle the callback URL

    If you are using the web platform, you need to create an endpoint to handle the callback URL and send it back to the application using the postMessage API.

    callback.html
    <!doctype html>
    <title>Authentication complete</title>
    <p>Authentication is complete. If this does not happen automatically, please close the window.</p>
    <script>
      function postAuthenticationMessage() {
        const message = {
          'flutter-web-auth-2': window.location.href,
        };

        if (window.opener) {
          window.opener.postMessage(message, window.location.origin);
          window.close();
        } else if (window.parent && window.parent !== window) {
          window.parent.postMessage(message, window.location.origin);
        } else {
          localStorage.setItem('flutter-web-auth-2', window.location.href);
          window.close();
        }
      }

      postAuthenticationMessage();
    </script>

Please check the setup guide in the flutter_web_auth_2 package for more details.

Integration​

Init LogtoClient​

Import the logto_dart_sdk package and initialize the LogtoClient instance at the root of your application.

lib/main.dart
import 'package:logto_dart_sdk/logto_dart_sdk.dart';
import 'package:http/http.dart' as http;

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      title: 'Flutter Demo',
      home: MyHomePage(title: 'Logto Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({Key? key, required this.title}) : super(key: key);
  final String title;

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  late LogtoClient logtoClient;

  void render() {
    // state change
  }

  // LogtoConfig
  final logtoConfig = const LogtoConfig(
    endpoint: "<your-logto-endpoint>",
    appId: "<your-app-id>"
  );

  void _init() {
    logtoClient = LogtoClient(
      config: logtoConfig,
      httpClient: http.Client(), // Optional http client
    );
    render();
  }

  @override
  void initState() {
    super.initState();
    _init();
  }

  // ...
}

Implement sign-in​

Before we dive into the details, here's a quick overview of the end-user experience. The sign-in process can be simplified as follows:

  1. Your app invokes the sign-in method.
  2. The user is redirected to the Logto sign-in page. For native apps, the system browser is opened.
  3. The user signs in and is redirected back to your app (configured as the redirect URI).

Regarding redirect-based sign-in​

  1. This authentication process follows the OpenID Connect (OIDC) protocol, and Logto enforces strict security measures to protect user sign-in.
  2. If you have multiple apps, you can use the same identity provider (Logto). Once the user signs in to one app, Logto will automatically complete the sign-in process when the user accesses another app.

To learn more about the rationale and benefits of redirect-based sign-in, see Logto sign-in experience explained.

Before starting, you need to add a redirect URI in the Admin Console for your application.

Let's switch to the Application details page of Logto Console. Add a Redirect URI io.logto://callback and click "Save changes".

Redirect URI in Logto Console
  • For iOS, the redirect URI scheme does not really matter since the ASWebAuthenticationSession class will listen to the redirect URI regardless of if it's registered.
  • For Android, the redirect URI scheme must be registered in the AndroidManifest.xml file.

After the redirect URI is configured, we add a sign-in button to your page, which will call logtoClient.signIn API to invoke the Logto sign-in flow:

lib/main.dart
class _MyHomePageState extends State<MyHomePage> {
  // ...
  final redirectUri = 'io.logto://callback';

  @override
  Widget build(BuildContext context) {
    // ...

    Widget signInButton = TextButton(
      onPressed: () async {
        await logtoClient.signIn(redirectUri);
        render();
      },
      child: const Text('Sign In'),
    );

    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            SelectableText('My Demo App'),
            signInButton,
          ],
        ),
      ),
    );
  }
}

Implement sign-out​

Let's switch to the Application details page of Logto Console. Add a Post Sign-out Redirect URI io.logto://callback and click "Save changes".

Post Sign-out Redirect URI in Logto Console

Post Sign-outRedirect URI is an OAuth 2.0 concept which implies the location should redirect after signing out.

Now let's add a sign-out button on the main page so users can sign out from your application.

lib/main.dart
class _MyHomePageState extends State<MyHomePage> {
  // ...

  final postSignOutRedirectUri = 'io.logto//home';

  @override
  Widget build(BuildContext context) {
    // ...

    Widget signOutButton = TextButton(
      onPressed: () async {
        await logtoClient.signOut(postSignOutRedirectUri);
        render();
      },
      child: const Text('Sign Out'),
    );

    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            SelectableText('My Demo App'),
            signInButton,
            signOutButton,
          ],
        ),
      ),
    );
  }
}

Handle authentication status​

Logto SDK provides an asynchronous method to check the authentication status. The method is logtoClient.isAuthenticated. The method returns a boolean value, true if the user is authenticated, otherwise false.

In the example we conditionally render the sign-in and sign-out buttons based on the authentication status. Now let's update the render method in our Widget to handle the state change:

lib/main.dart
class _MyHomePageState extends State<MyHomePage> {
  // ...
  bool? isAuthenticated = false;

  void render() {
    setState(() async {
      isAuthenticated = await logtoClient.isAuthenticated;
    });
  }

  @override
  Widget build(BuildContext context) {
    // ...

    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            SelectableText('My Demo App'),
            isAuthenticated == true ? signOutButton : signInButton,
          ],
        ),
      ),
    );
  }
}

Checkpoint: Test your application​

Now, you can test your application:

  1. Run your application, you will see the sign-in button.
  2. Click the sign-in button, the SDK will init the sign-in process and redirect you to the Logto sign-in page.
  3. After you signed in, you will be redirected back to your application and see the sign-out button.
  4. Click the sign-out button to clear token storage and sign out.

Add Twilio connector​

SMS connector is a method used to send one-time passwords (OTPs) for authentication. It enables Phone number verification to support passwordless authentication, including SMS-based registration, sign-in, two-factor authentication (2FA), and account recovery. You can easily connect Twilio as your SMS provider. With the Logto SMS connector, you can set this up in just a few minutes.

To add a SMS connector, simply follow these steps:

  1. Navigate to Console > Connector > Email and SMS connectors.
  2. To add a new SMS connector, click the "Set up" button and select "Twilio".
  3. Review the README documentation for your selected provider.
  4. Complete the configuration fields in the "Parameter Configuration" section.
  5. Customize the SMS template using the JSON editor.
  6. Test your configuration by sending a verification code to your Phone number.

Connector tab

note:

If you are following the in-place Connector guide, you can skip the next section.

Set up Twilio SMS connector​

Register Twilio account​

Create a new account on Twilio. (Jump to the next step if you already have one.)

Set up senders' phone numbers​

Go to the Twilio console page and sign in with your Twilio account.

Purchase a phone number under "Phone Numbers" -> "Manage" -> "Buy a number".

tip:

Sometimes you may encounter the situation that SMS service is not supported in specific countries or areas. Pick a number from other regions to bypass.

Once we have a valid number claimed, nav to the "Messaging" -> "Services". Create a new Message Service by clicking on the button.

Give a friendly service name and choose Notify my users as our service purpose. Following the next step, choose Phone Number as Sender Type, and add the phone number we just claimed to this service as a sender.

note:

Each phone number can only be linked with one messaging service.

Get account credentials​

We will need the API credentials to make the connector work. Let's begin from the Twilio console page.

Click on the "Account" menu in the top-right corner, then go to the "API keys & tokens" page to get your Account SID and Auth token.

Back to "Messaging" -> "Services" settings page starting from the sidebar, and find the Sid of your service.

Compose the connector JSON​

Fill out the accountSID, authToken and fromMessagingServiceSID fields with Account SID, Auth token and Sid of the corresponding messaging service.

You can add multiple SMS connector templates for different cases. Here is an example of adding a single template:

  • Fill out the content field with arbitrary string-typed contents. Do not forget to leave {{code}} placeholder for random verification code.
  • Fill out the usageType field with either Register, SignIn, ForgotPassword, Generic for different use cases. In order to enable full user flows, templates with usageType Register, SignIn, ForgotPassword and Generic are required.

Test Twilio SMS connector​

You can enter a phone number and click on "Send" to see whether the settings can work before "Save and Done".

That's it. Don't forget to Enable connector in sign-in experience.

Config types​

NameType
accountSIDstring
authTokenstring
fromMessagingServiceSIDstring
templatesTemplates[]
Template PropertiesTypeEnum values
contentstringN/A
usageTypeenum string'Register' | 'SignIn' | 'ForgotPassword' | 'Generic'

Save your configuration​

Double check you have filled out necessary values in the Logto connector configuration area. Click "Save and Done" (or "Save changes") and the Twilio connector should be available now.

Enable Twilio connector in Sign-in Experience​

Once you create a connector successfully, you can enable phone number-based passwordless login and registration.

  1. Navigate to Console > Sign-in experience > Sign-up and sign-in.
  2. Set up sign-up methods (Optional):
    1. Select "Phone number" or "Email or phone number" as the sign-up identifier.
    2. "Verify at sign-up" is forced to be enabled. You can also enable "Create a password" on registration.
  3. Set up sign-in methods:
    1. Select Phone number as one of sign-in identifiers. You can provide multiple available identifiers (email, phone number, and username).
    2. Select "Verification code" and / or "Password" as the authentication factor.
  4. Click "Save changes" and test it in "Live preview".

Sign-in Experience tab

In addition to registration and login via OTPs, you can also have password recovery and -based security verification enabled, as well as linking Phone number to profile. See End-user flows for more details.

Testing and Validation​

Return to your Flutter app. You should now be able to sign in with Twilio. Enjoy!

Further readings​

End-user flows: Logto provides a out-of-the-box authentication flows including MFA and enterprise SSO, along with powerful APIs for flexible implementation of account settings, security verification, and multi-tenant experience.

Authorization: Authorization defines the actions a user can do or resources they can access after being authenticated. Explore how to protect your API for native and single-page applications and implement Role-based Access Control (RBAC).

Organizations: Particularly effective in multi-tenant SaaS and B2B apps, the organization feature enable tenant creation, member management, organization-level RBAC, and just-in-time-provisioning.

Customer IAM series Our serial blog posts about Customer (or Consumer) Identity and Access Management, from 101 to advanced topics and beyond.