How to build SMTP Email passwordless sign-in with Capacitor JS

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 SMTP sign-in experience (user authentication) with Capacitor JS and Logto.

Prerequisites

A running Logto instance. Check out the introduction page to get started.
Basic knowledge of Capacitor JS.
A usable SMTP 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:

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.
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 "Capacitor JS" framework card to start creating your application.
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 Capacitor JS with Logto

tip:

The following demonstration is built on Capacitor JS 5.0.6.

Installation

Install Logto SDK and peer dependencies via your favorite package manager:

npm
Yarn
pnpm

npm i @logto/capacitor
npm i @capacitor/browser @capacitor/app @capacitor/preferences

yarn add @logto/capacitor
yarn add @capacitor/browser @capacitor/app @capacitor/preferences

pnpm add @logto/capacitor
pnpm add @capacitor/browser @capacitor/app @capacitor/preferences

The @logto/capacitor package is the SDK for Logto. The remaining packages are its peer dependencies.

Init Logto client

Add the following code to your Capacitor project:

import LogtoClient, { type LogtoConfig } from '@logto/capacitor';

const logtoConfig: LogtoConfig = {
  endpoint: '<your-logto-endpoint>',
  appId: '<your-application-id>',
};

const logtoClient = new LogtoClient(config);

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.

Now, let's configure the redirect URI. The redirect URI is used to redirect the user back to your application after the authentication flow.

Ensure that the URI redirects to the Capacitor app, for example, com.example.app://callback. The value may vary depending on your Capacitor app configuration. For more details, see Capacitor Deep Links.

Then, add the following code to the onClick handler of the sign-in button:

const onClick = async () => {
  await logtoClient.signIn('com.example.app://callback');
  console.log(await logtoClient.isAuthenticated()); // true
  console.log(await logtoClient.getIdTokenClaims()); // { sub: '...', ... }
};

Implement sign-out

Since Capacitor leverages the Safari View Controller on iOS and Chrome Custom Tabs on Android, the authentication state can be persisted for a while. However, sometimes the user may want to sign out of the application immediately. In this case, we can use the signOut method to sign out the user:

const onClick = async () => {
  await logtoClient.signOut();
  console.log(await logtoClient.isAuthenticated()); // false
};

The signOut method has an optional parameter for the post sign-out redirect URI. If it's not provided, the user will be redirected to the Logto sign-out page.

The user needs to click "Done" to close the web view and return to the Capacitor app. If you want to automatically redirect the user back to the Capacitor app, you can provide the post sign-out redirect URI, for instance, com.example.app://callback/sign-out.

Ensure that the post sign-out redirect URI can redirect to the Capacitor app. Then add the following code to the onClick handler of the sign-out button:

const onClick = async () => {
  await logtoClient.signOut('com.example.app://callback/sign-out');
};

Checkpoint: Trigger the authentication flow

Run the Capacitor app and click the sign-in button. A browser window will open, redirecting to the Logto sign-in page.

If the user closes the browser window without completing the authentication flow, the Capacitor app will receive a LogtoClientError.

Add SMTP connector

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

To add a Email connector, simply follow these steps:

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

note:

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

Set up SMTP email connector

Set up SMTP connector

SMTP is a transmission protocol that is not exclusive to some specific email service providers but can work with all providers.

We are now offering guides on how to use the SMTP connector to send emails following providers for your better understanding:

Gmail is the most popular email service vendor worldwide.
Aliyun direct mail and SendGrid mail. Some of you might be familiar with these two email service providers because Logto Team provided corresponding connectors; you will likely have a general idea of them.

We hope you can figure out all other email vendors' setups with the following examples 🚀

Set up for Gmail use

You can get a new Gmail account at Gmail, or you can use an existing account if you have one.

A Gmail official post shows how to determine required properties' values to operate Gmail via an SMTP connector.

Integrate with SendGrid SMTP API

Initially, we assume that you already have a SendGrid account. If not, create a new account at the SendGrid website.

You can find a step-by-step guide on "Integrating with the SMTP API".

Developers can access sender details on the "Sender Management".

Configure with Aliyun direct mail account

Follow the Send emails using SMTP guide and finish those 'tasks' to get those required settings and information.

You can go to SMTP service address page to choose a proper SMTP service address host and port number.

To check "Sender Addresses", you can find the entrance on the left-side navigation pane on DirectMail console. You should see Sender address and SMTP Password here.

note:

Only one sample template is provided in the previous cases to keep things simple. You should add more templates for other use cases. You should change values wrapped with "<" and ">" according to your Gmail, SendGrid or Aliyun account settings and choose to keep other fields w/o "<" and ">". Add {{code}} as a placeholder in templates' content to show random verification code in sending emails.

Test SMTP connector

You can type in an email address 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

Name	Type
host	string
port	string
fromEmail	string
templates	Template[]

Template Properties	Type	Enum values
subject	string	N/A
content	string	N/A
usageType	enum string	'Register' \| 'SignIn' \| 'ForgotPassword' \| 'Generic'
contentType	enum string	'text/plain' \| 'text/html'

Username and password Auth Options

Name	Type	Enum values
user	string	N/A
pass	string	N/A
type	enum string (OPTIONAL)	'login'

You can also configure OAuth2 Auth Options and other advanced configurations. See here for more details.

We gave an example config with all configurable parameters in the text box to help you to set up own configuration. (You are responsible to the configuration, some values are for demonstration purpose and may not fit your use case.)

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 SMTP connector should be available now.

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

Navigate to Console > Sign-in experience > Sign-up and sign-in.
Set up sign-up methods (Optional):
1. Select "Email address" 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.
Set up sign-in methods:
1. Select Email address 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.
Click "Save changes" and test it in "Live preview".

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

Testing and Validation

Return to your Capacitor JS app. You should now be able to sign in with SMTP. Enjoy!

Create an application in Logto​

Integrate Capacitor JS with Logto​

Installation​

Init Logto client​

Implement sign-in​

Regarding redirect-based sign-in​

Implement sign-out​

Checkpoint: Trigger the authentication flow​

Add SMTP connector​

Set up SMTP email connector​

Set up SMTP connector​

Set up for Gmail use​

Integrate with SendGrid SMTP API​

Configure with Aliyun direct mail account​

Test SMTP connector​

Config types​

Save your configuration​

Enable SMTP connector in Sign-in Experience​

Testing and Validation​

Further readings​