How to build OAuth2 sign-in with iOS Swift and Logto

December 22, 2024 · 2 min read

The better identity infrastructure for developers

For our new friends:

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 iOS Swift and Logto.

Prerequisites

A running Logto instance. Check out the introduction page to get started.
Basic knowledge of iOS Swift.
A usable OAuth2 account.

Create an application in Logto

In you browser, open a new tab and enter the link of Logto Admin Console.

Get Started

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

Framework List

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 "iOS(Swift)" 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

Add Logto SDK as a dependency

Use the following URL to add Logto SDK as a dependency in Swift Package Manager.

https://github.com/logto-io/swift.git

Since Xcode 11, you can directly import a Swift package w/o any additional tool.

We do not support Carthage and CocoaPods at the time due to some technical issues.

Carthage

Carthage needs a xcodeproj file to build, but swift package generate-xcodeproj will report a failure since we are using binary targets for native social plugins. We will try to find a workaround later.

CocoaPods

CocoaPods does not support local dependency and monorepo, thus it's hard to create a .podspec for this repo.

Init LogtoClient

Initialize the client by creating a LogtoClient instance with a LogtoConfig object.

ContentView.swift
import Logto
import LogtoClient

let config = try? LogtoConfig(
  endpoint: "<your-logto-endpoint>", // E.g. http://localhost:3001
  appId: "<your-app-id>"
)
let client = LogtoClient(useConfig: config)

info:

By default, we store credentials like ID Token and Refresh Token in the Keychain. Thus the user doesn't need to sign in again when he returns.

To turn off this behavior, set usingPersistStorage to false:

let config = try? LogtoConfig(
  // ...
  usingPersistStorage: false
)

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).

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.

Configure redirect URI

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

info:

The Redirect URI in iOS SDK is only for internal use. There's NO NEED to add a Custom URL Scheme until a connector asks.

note:

Before calling .signInWithBrowser(redirectUri:), make sure you have correctly configured Redirect URI in Admin Console.

You can use client.signInWithBrowser(redirectUri:) to sign in the user and client.signOut() to sign out the user.

For example, in a SwiftUI app:

ContentView.swift
struct ContentView: View {
  @State var isAuthenticated: Bool

  init() {
    isAuthenticated = client.isAuthenticated
  }

  var body: some View {
    VStack {
      if isAuthenticated {
        Button("Sign Out") {
          Task { [self] in
            await client.signOut()
            isAuthenticated = false
          }
        }
      } else {
        Button("Sign In") {
          Task { [self] in
            do {
              try await client.signInWithBrowser(redirectUri: "${
                props.redirectUris[0] ?? 'io.logto://callback'
              }")
              isAuthenticated = true
            } catch let error as LogtoClientErrors.SignIn {
              // error occured during sign in
            } catch {
              // other errors
            }
          }
        }
      }
    }
  }
}

Test your integration:

Open your iOS app to test if the integration works. When you click the "Sign In" button, the page should be redirected to a Logto sign-in page, and you should be able to create a new account by entering username and password and complete the sign-in process.

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 about customConfig.

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
email	string	false	email
phone	string	false	phone

Reference

The OAuth 2.0 2.0 Authorization Framework

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.

Switch to the "Sign-in experience" tab, then click the "Sign-up and sign-in" tab.

note:

If it's the first time you enter the tab, you will see a quick introduction about Sign-in Experience and its basic configuration.

Sign-in Experience tab

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.

Save changes

Finally, click "Save changes" on the bottom right corner.

Testing and Validation

Return to your iOS Swift app. You should now be able to sign in with OAuth2. Enjoy!

Create an application in Logto​

Choose your application type​

Enter application name​

Integrate Logto SDK​

Add Logto SDK as a dependency​

Carthage​

CocoaPods​

Init LogtoClient​

Sign in​

Regarding redirect-based sign-in​

Configure redirect URI​

Sign-in and sign-out​

Add OAuth2 connector​

Set up Standard OAuth 2.0 app​

Create your OAuth 2.0 app​

Configure your connector​

Config types​

Reference​

Save your configuration​

Enable OAuth2 connector in Sign-in Experience​

Testing and Validation​

Further readings​