How to build Mailgun Email passwordless sign-in with Go

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 Mailgun sign-in experience (user authentication) with Go and Logto.

Prerequisites

A running Logto instance. Check out the introduction page to get started.
Basic knowledge of Go.
A usable Mailgun 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 Traditional web 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 "Traditional web" section or filter all the available "Traditional web" frameworks using the quick filter checkboxes on the left. Click the "Go" 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 Go with Logto

tip:

The following demonstration is built upon the Gin Web Framework. You may also integrate Logto into other frameworks by taking the same steps.
The Go sample project is available on our Go SDK repo.

Installation

Execute in the project root directory:

go get github.com/logto-io/go

Add the github.com/logto-io/go/client package to your application code:

main.go
// main.go
package main

import (
	"github.com/gin-gonic/gin"
	// Add dependency
	"github.com/logto-io/go/client"
)

func main() {
	router := gin.Default()
	router.GET("/", func(c *gin.Context) {
		c.String(200, "Hello Logto!")
	})
	router.Run(":3000")
}

Create a session storage

In traditional web applications, the user authentication information will be stored in the user session.

Logto SDK provides a Storage interface, you can implement a Storage adapter based on your web framework so that the Logto SDK can store user authentication information in the session.

note:

We do NOT recommend using cookie-based sessions, as user authentication information stored by Logto may exceed the cookie size limit. In this example, we use memory-based sessions. You can use Redis, MongoDB, and other technologies in production to store sessions as needed.

The Storage type in the Logto SDK is as follows:

github.com/logto-io/client/storage.go
package client

type Storage interface {
	GetItem(key string) string
	SetItem(key, value string)
}

We use github.com/gin-contrib/sessions middleware as an example to demonstrate this process.

Apply the middleware to the application, so that we can get the user session by the user request context in the route handler:

main.go
package main

import (
	"github.com/gin-contrib/sessions"
	"github.com/gin-contrib/sessions/memstore"
	"github.com/gin-gonic/gin"
	"github.com/logto-io/go/client"
)

func main() {
	router := gin.Default()

	// We use memory-based session in this example
	store := memstore.NewStore([]byte("your session secret"))
	router.Use(sessions.Sessions("logto-session", store))

	router.GET("/", func(ctx *gin.Context) {
		// Get user session
		session := sessions.Default(ctx)
		// ...
		ctx.String(200, "Hello Logto!")
	})
	router.Run(":3000")
}

Create a session_storage.go file, define a SessionStorage and implement the Logto SDK's Storage interfaces:

session_storage.go
package main

import (
	"github.com/gin-contrib/sessions"
)

type SessionStorage struct {
	session sessions.Session
}

func (storage *SessionStorage) GetItem(key string) string {
	value := storage.session.Get(key)
	if value == nil {
		return ""
	}
	return value.(string)
}

func (storage *SessionStorage) SetItem(key, value string) {
	storage.session.Set(key, value)
	storage.session.Save()
}

Now, in the route handler, you can create a session storage for Logto:

session := sessions.Default(ctx)
sessionStorage := &SessionStorage{session: session}

Init LogtoClient

First, create a Logto config:

main.go
func main() {
	// ...
	logtoConfig := &client.LogtoConfig{
		Endpoint:  "<your-logto-endpoint>", // E.g. http://localhost:3001
		AppId:     "<your-application-id>",
		AppSecret: "<your-application-secret>",
	}
	// ...
}

tip:

You can find and copy "App Secret" from application details page in Admin Console:

Then, you can create a LogtoClient for each user request with the Logto config above:

main.go
func main() {
	// ...

	router.GET("/", func(ctx *gin.Context) {
		// Create LogtoClient
		session := sessions.Default(ctx)
		logtoClient := client.NewLogtoClient(
			logtoConfig,
			&SessionStorage{session: session},
		)

		// Use Logto to control the content of the home page
		authState := "You are not logged in to this website. :("

		if logtoClient.IsAuthenticated() {
			authState = "You are logged in to this website! :)"
		}

		homePage := `<h1>Hello Logto</h1>` +
			"<div>" + authState + "</div>"

		ctx.Data(http.StatusOK, "text/html; charset=utf-8", []byte(homePage))
	})

	// ...
}

After the redirect URI is configured, we add a sign-in route to handle the sign-in request and also add an sign-in link on the home page:

main.go
func main() {
	// ...

	// Add a link to perform a sign-in request on the home page
	router.GET("/", func(ctx *gin.Context) {
		// ...
		homePage := `<h1>Hello Logto</h1>` +
			"<div>" + authState + "</div>" +
			// Add link
			`<div><a href="/sign-in">Sign In</a></div>`

		ctx.Data(http.StatusOK, "text/html; charset=utf-8", []byte(homePage))
	})

	// Add a route for handling sign-in requests
	router.GET("/sign-in", func(ctx *gin.Context) {
		session := sessions.Default(ctx)
		logtoClient := client.NewLogtoClient(
			logtoConfig,
			&SessionStorage{session: session},
		)

		// The sign-in request is handled by Logto.
		// The user will be redirected to the Redirect URI on signed in.
		signInUri, err := logtoClient.SignIn("http://localhost:3000/callback")
		if err != nil {
			ctx.String(http.StatusInternalServerError, err.Error())
			return
		}

		// Redirect the user to the Logto sign-in page.
		ctx.Redirect(http.StatusTemporaryRedirect, signInUri)
	})

	// ...
}

Now, when your user visit http://localhost:3000/sign-in, the user will be redirected to the Logto sign-in page.

Implement the callback route

When the user signs in successfully on the Logto sign-in page, Logto will redirect the user to the Redirect URI.

Since the redirect URI is http://localhost:3000/callback, we add the /callback route to handle the callback after signing in.

main.go
func main() {
	// ...

	// Add a route for handling sign-in callback requests
	router.GET("/callback", func(ctx *gin.Context) {
		session := sessions.Default(ctx)
		logtoClient := client.NewLogtoClient(
			logtoConfig,
			&SessionStorage{session: session},
		)

		// The sign-in callback request is handled by Logto
		err := logtoClient.HandleSignInCallback(ctx.Request)
		if err != nil {
			ctx.String(http.StatusInternalServerError, err.Error())
			return
		}

		// Jump to the page specified by the developer.
		// This example takes the user back to the home page.
		ctx.Redirect(http.StatusTemporaryRedirect, "/")
	})

	// ...
}

Implement sign-out route

Similar to the sign-in flow, when the user signs out, Logto will redirect the user to the post sign-out redirect URI.

Now, let's add the sign-out route to handle the sign-out request and also add a sign-out link on the home page:

main.go
func main() {
	// ...

	// Add a link to perform a sign-out request on the home page
	router.GET("/", func(ctx *gin.Context) {
		// ...
		homePage := `<h1>Hello Logto</h1>` +
			"<div>" + authState + "</div>" +
			`<div><a href="/sign-in">Sign In</a></div>` +
			// Add link
			`<div><a href="/sign-out">Sign Out</a></div>`

		ctx.Data(http.StatusOK, "text/html; charset=utf-8", []byte(homePage))
	})

	// Add a route for handling signing out requests
	router.GET("/sign-out", func(ctx *gin.Context) {
		session := sessions.Default(ctx)
		logtoClient := client.NewLogtoClient(
			logtoConfig,
			&SessionStorage{session: session},
		)

		// The sign-out request is handled by Logto.
		// The user will be redirected to the Post Sign-out Redirect URI on signed out.
		signOutUri, signOutErr := logtoClient.SignOut("http://localhost:3000")

		if signOutErr != nil {
			ctx.String(http.StatusOK, signOutErr.Error())
			return
		}

		ctx.Redirect(http.StatusTemporaryRedirect, signOutUri)
	})

	// ...
}

After the user makes a signing-out request, Logto will clear all user authentication information in the session.

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 token storage and sign out.

Add Mailgun 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 Mailgun 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 "Mailgun".
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 Mailgun email connector

Prerequisites

A Mailgun account
An API key from your Mailgun account, requires the permission to send messages (emails). See Where Can I Find My API Key and SMTP Credentials? for more information.

Basic configuration

Fill out the endpoint field when you are using a different Mailgun API endpoint, for example, EU region should be https://api.eu.mailgun.net. The default value is https://api.mailgun.net.
Fill out the domain field with the domain you have registered in your Mailgun account. This value can be found in the Domains section of the Mailgun dashboard. The domain should be in the format example.com, without the https:// or http:// prefix.
Fill out the apiKey field with the API key you have generated in your Mailgun account.
Fill out the from field with the email address you want to send emails from. This email address must be registered in your Mailgun account. The email address should be in the format Sender Name \<[email protected]>.

Deliveries

Config object

The "Deliveries" section allows you to configure the content of the emails to be sent in different scenarios. It is a JSON key-value map where the key is the usage type and the value is an object containing the content config for the email to be sent.

{
  "<usage-type>": {
    // ...
  }
}

Usage types

The following usage types are supported:

Register: The email to be sent when a user is registering.
SignIn: The email to be sent when a user is signing in.
ForgotPassword: The email to be sent when a user is resetting their password.
Generic: The email to be sent when a user is performing a generic action, for example, testing the email connector.

note:

If the usage type is not specified in the deliveries config, the generic email will be sent. If the generic email is not specified, the connector will return an error.

Content config

The connector supports both direct HTML content and Mailgun template. You can use one of them for each usage type.

In both subject and content, you can use the {{code}} placeholder to insert the verification code.

To use direct HTML content, fill out the following fields:

subject: The subject of the email to be sent.
replyTo: The email address to be used as the reply-to address.
html: (Required) The HTML content of the email to be sent.
text: The plain text version of the email to be sent.

To use Mailgun template, fill out the following fields:

subject: The subject of the email to be sent.
replyTo: The email address to be used as the reply-to address.
template: (Required) The name of the Mailgun template to be used.
variables: The variables to be passed to the Mailgun template. Should be a JSON key-value map since it will be stringified before sending to Mailgun. Note there's no need to include the code variable since it will be automatically added by the connector.

Example

The following is an example of the deliveries config:

{
  "Register": {
    "subject": "{{code}} is your verification code",
    "replyTo": "Foo <[email protected]>",
    "html": "<h1>Welcome to Logto</h1><p>Your verification code is {{code}}.</p>",
    "text": "Welcome to Logto. Your verification code is {{code}}."
  },
  "SignIn": {
    "subject": "Welcome back to Logto",
    "replyTo": "Foo <[email protected]>",
    "template": "logto-sign-in",
    "variables": {
      "bar": "baz"
    }
  }
}

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 Mailgun 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 Go app. You should now be able to sign in with Mailgun. Enjoy!

Create an application in Logto​

Integrate Go with Logto​

Installation​

Create a session storage​

Init LogtoClient​

Implement sign-in route​

Implement the callback route​

Implement sign-out route​

Checkpoint: Test your application​

Add Mailgun connector​

Set up Mailgun email connector​

Prerequisites​

Basic configuration​

Deliveries​

Config object​

Usage types​

Content config​

Example​

Save your configuration​

Enable Mailgun connector in Sign-in Experience​

Testing and Validation​

Further readings​

Create an application in Logto

Integrate Go with Logto

Installation

Create a session storage

Init LogtoClient

Implement sign-in route

Implement the callback route

Implement sign-out route

Checkpoint: Test your application

Add Mailgun connector

Set up Mailgun email connector

Prerequisites

Basic configuration

Deliveries

Config object

Usage types

Content config

Example

Save your configuration

Enable Mailgun connector in Sign-in Experience

Testing and Validation

Further readings