Every app needs authentication and authorization. Logto is an Auth0 alternative designed for modern apps and SaaS products.
In this article, we will go through the steps to quickly build the OAuth2 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 OAuth2 account.
Create an application in Logto
In you browser, open a new tab and enter the link of Logto Admin Console.
Once the page is loaded, in the "Get Started" section click the View all
link to open the application framework list page.
Choose your application type
In the opening modal, scroll to 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.
Enter application name
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
- 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 and our GitHub repository.
- The SDK is compatible with Android, and iOS platforms only.
- The SDK v1.x is compatible with Dart 2.x. For SDK v2.x, you need to update your Dart version to 3.x or higher.
Installation
- pub.dev
- GitHub
You can install the logto_dart_sdk package
directly using the pub package manager.
Run the following command under your project root:
flutter pub get logto_dart_sdk
If you prefer to fork your own version of the SDK, you can clone the repository directly from GitHub.
git clone https://github.com/logto-io/dart
Modules
The logto_dart_sdk
includes two main modules:
-
logto_core.dart This core module provides the basic functions and interfaces for the Logto SDK.
-
logto_client.dart This client module offers a high-level Logto client class for interacting with the Logto server.
Dependency and configurations
Dependency and configurations
This SDK has the following dependencies, some require additional configurations:
flutter_secure_storage
We use 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.
android {
...
defaultConfig {
...
minSdkVersion 18
...
}
}
Disable autobackup
By default Android may backup data on Google Drive automatically. It can cause exception java.security.InvalidKeyException:Failed to unwrap key
.
To avoid this, you can disable auto backup for your app or exclude sharedprefs
from the FlutterSecureStorage
.
-
To disable auto backup, go to your app manifest file and set the
android:allowBackup
andandroid:fullBackupContent
attributes tofalse
.AndroidManifest.xml<manifest ... >
...
<application
android:allowBackup="false"
android:fullBackupContent="false"
...
>
...
</application>
</manifest> -
Exclude
sharedprefs
fromFlutterSecureStorage
.If you need to keep the
android:fullBackupContent
for your app rather than disabling it, you can exclude thesharedprefs
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 theres/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
flutter_web_auth is used behind Logto's flutter SDK. We rely on its webview-based interaction interface to authenticate users.
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.
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.
<activity android:name="com.linusu.flutter_web_auth.CallbackActivity" android:exported="true">
<intent-filter android:label="flutter_web_auth">
<action android:name="android.intent.action.VIEW"/>
<category android:name="android.intent.category.DEFAULT"/>
<category android:name="android.intent.category.BROWSABLE"/>
<data android:scheme="io.logto"/>
</intent-filter>
</activity>
http.dart
Since the SDK need to make network requests, you will need to pass in a HTTP client to the SDK. You can use the default http.Client
from http.dart or create your own http.Client
with custom configurations.
import 'package:http/http.dart' as http;
Integration
Init LogtoClient
Import the logto_dart_sdk
package and initialize the LogtoClient
instance at the root of your application.
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);
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;
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();
}
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:
- Your app invokes the sign-in method.
- The user is redirected to the Logto sign-in page. For native apps, the system browser is opened.
- The user signs in and is redirected back to your app (configured as the redirect URI).
Regarding redirect-based sign-in
- This authentication process follows the OpenID Connect (OIDC) protocol, and Logto enforces strict security measures to protect user sign-in.
- 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".
- 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:
class _MyHomePageState extends State<MyHomePage> {
// ...
final redirectUri = 'io.logto://callback';
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
Now let's add a sign-out button on the main page so users can sign out from your application.
class _MyHomePageState extends State<MyHomePage> {
// ...
Widget build(BuildContext context) {
// ...
Widget signOutButton = TextButton(
onPressed: () async {
await logtoClient.signOut();
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:
class _MyHomePageState extends State<MyHomePage> {
// ...
bool? isAuthenticated = false;
void render() {
setState(() async {
isAuthenticated = await logtoClient.isAuthenticated;
});
}
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:
- Run your application, you will see the sign-in button.
- Click the sign-in button, the SDK will init the sign-in process and redirect you to the Logto sign-in page.
- After you signed in, you will be redirected back to your application and see the sign-out button.
- Click the sign-out button to clear local storage and sign out.
Add OAuth2 connector
To add a social connector, go to the "Connector" tab in the Admin Console, then click on "Social connectors". From there, click "Add social connector".
In the openning modal, select "OAuth2" and click "Next".
On the next page, you will see a two-column layout with the README content on the left and configuration on the right.
Feel free to follow the README file in place or read the following section to complete the configuration process. If you follow the in-place guide, you can skip the next section.
Set up Standard OAuth 2.0 app
Create your OAuth 2.0 app
When you open this page, we believe you already know which social identity provider you want to connect to. The first thing to do is to confirm that the identity provider supports the OAuth 2.0 protocol, which is a prerequisite for configuring a valid connector. Then, follow the identity provider's instructions to register and create the relevant app for OAuth 2.0 authorization.
Configure your connector
We ONLY support "Authorization Code" grant type for security consideration and it can perfectly fit Logto's scenario.
clientId
and clientSecret
can be found at your OAuth 2.0 apps details page.
clientId: The client ID is a unique identifier that identifies the client application during registration with the authorization server. This ID is used by the authorization server to verify the identity of the client application and to associate any authorized access tokens with that specific client application.
clientSecret: The client secret is a confidential key that is issued to the client application by the authorization server during registration. The client application uses this secret key to authenticate itself with the authorization server when requesting access tokens. The client secret is considered confidential information and should be kept secure at all times.
scope: The scope parameter is used to specify the set of resources and permissions that the client application is requesting access to. The scope parameter is typically defined as a space-separated list of values that represent specific permissions. For example, a scope value of "read write" might indicate that the client application is requesting read and write access to a user's data.
You are expected to find authorizationEndpoint
, tokenEndpoint
and userInfoEndpoint
in social vendor's documentation.
authenticationEndpoint: This endpoint is used to initiate the authentication process. The authentication process typically involves the user logging in and granting authorization for the client application to access their resources.
tokenEndpoint: This endpoint is used by the client application to obtain an access token that can be used to access the requested resources. The client application typically sends a request to the token endpoint with a grant type and authorization code to receive an access token.
userInfoEndpoint: This endpoint is used by the client application to obtain additional information about the user, such as their fullname, email address or profile picture. The user info endpoint is typically accessed after the client application has obtained an access token from the token endpoint.
Logto also provide a profileMap
field that users can customize the mapping from the social vendors' profiles which are usually not standard. The keys are Logto's standard user profile field names and corresponding values should be social profiles' field names. In current stage, Logto only concern 'id', 'name', 'avatar', 'email' and 'phone' from social profile, only 'id' is required and others are optional fields.
responseType
and grantType
can ONLY be FIXED values with authorization code grant type, so we make them optional and default values will be automatically filled.
For example, you can find Google user profile response and hence its profileMap
should be like:
{
"id": "sub",
"avatar": "picture"
}
ℹ️ Note
We provided an OPTIONAL
customConfig
key to put your customize parameters. Each social identity provider could have their own variant on OAuth 2.0 standard protocol. If your desired social identity provider strictly stick to OAuth 2.0 standard protocol, the you do not need to care aboutcustomConfig
.
Config types
Name | Type | Required |
---|---|---|
authorizationEndpoint | string | true |
userInfoEndpoint | string | true |
clientId | string | true |
clientSecret | string | true |
tokenEndpointResponseType | enum | false |
responseType | string | false |
grantType | string | false |
tokenEndpoint | string | false |
scope | string | false |
customConfig | { [key: string]: string } | false |
profileMap | ProfileMap | false |
ProfileMap fields | Type | Required | Default value |
---|---|---|---|
id | string | false | id |
name | string | false | name |
avatar | string | false | avatar |
string | false | ||
phone | string | false | phone |
Reference
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 OAuth2 connector should be available now.
Enable OAuth2 connector in Sign-in Experience
Switch to the "Sign-in experience" tab, then click the "Sign-up and sign-in" tab.
If it's the first time you enter the tab, you will see a quick introduction about Sign-in Experience and its basic configuration.
Select "None" for the "Sign-up identifier" to provide minimum sign-up effort for OAuth2 sign-in, which may increase your conversion rate.
In the "Social sign-in" section, add "Add Social Connector" and choose "OAuth2". Then you should be able to see a button with text "Continue with OAuth2" in the preview section.
Finally, click "Save changes" on the bottom right corner.
Testing and Validation
Return to your Flutter app. You should now be able to sign in with OAuth2. Enjoy!
Further readings
Protect your API For native and single page apps, you'll need to call one or more API endpoints to retrieve and update data.
Learn more about identifying who's who and keeping your API secure.
User management We know you care about user management and activities, as we also do.
Learn more about how to know your users and see the figures like DAU and MAU graphically.
Localization From one regional business to a global corporate, the willingness to offer the best user experience won't change.
You can change current language phrases or add a new language without friction.
Customer IAM series Our serial blog posts about Customer (or Consumer) Identity and Access Management, from 101 to advanced topics and beyond.