How to build SMTP Email passwordless sign-in with Python

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 Python and Logto.

Prerequisites

A running Logto instance. Check out the introduction page to get started.
Basic knowledge of Python.
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 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 "Flask" 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 Flask with Logto

tip:

The example uses Flask, but the concepts are the same for other frameworks.
The Python sample project is available on our Python SDK repo.
Logto SDK leverages coroutines, remember to use await when calling async functions.

Installation

Execute in the project root directory:

pip install logto # or `poetry add logto` or whatever you use

Init LogtoClient

First, create a Logto config:

client.py
from logto import LogtoClient, LogtoConfig

client = LogtoClient(
    LogtoConfig(
        endpoint="https://you-logto-endpoint.app",  # Replace with your Logto endpoint
        appId="replace-with-your-app-id",
        appSecret="replace-with-your-app-secret",
    ),
)

tip:

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

Also replace the default memory storage with a persistent storage, for example:

client.py
from logto import LogtoClient, LogtoConfig, Storage
from flask import session
from typing import Union

class SessionStorage(Storage):
    def get(self, key: str) -> Union[str, None]:
        return session.get(key, None)

    def set(self, key: str, value: Union[str, None]) -> None:
        session[key] = value

    def delete(self, key: str) -> None:
        session.pop(key, None)

client = LogtoClient(
    LogtoConfig(...),
    storage=SessionStorage(),
)

See Storage for more details.

In your web application, add a route to properly handle the sign-in request from users. Let's use /sign-in as an example:

flask.py
@app.route("/sign-in")
async def sign_in():
  # Get the sign-in URL and redirect the user to it
  return redirect(await client.signIn(
      redirectUri="http://localhost:3000/callback",
  ))

Replace http://localhost:3000/callback with the callback URL you set in your Logto Console for this application.

If you want to show the sign-up page on the first screen, you can set interactionMode to signUp:

flask.py
@app.route("/sign-in")
async def sign_in():
  return redirect(await client.signIn(
      redirectUri="http://localhost:3000/callback",
      interactionMode="signUp", # Show the sign-up page on the first screen
  ))

Now, whenever your users visit http://localhost:3000/sign-in, it will start a new sign-in attempt and redirect the user to the Logto sign-in page.

Note Creating a sign-in route isn't the only way to start a sign-in attempt. You can always use the signIn method to get the sign-in URL and redirect the user to it.

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

To clean up the Python session and Logto session, a sign-out route can be implemented as follows:

flask.py
@app.route("/sign-out")
async def sign_out():
  return redirect(
      # Redirect the user to the home page after a successful sign-out
      await client.signOut(postLogoutRedirectUri="http://localhost:3000/")
  )

Handle authentication status

In Logto SDK, we can use client.isAuthenticated() to check the authentication status, if the user is signed in, the value will be true, otherwise, the value will be false.

Here we also implement a simple home page for demonstration:

If the user is not signed in, show a sign-in button;
If the user is signed in, show a sign-out button.

@app.route("/")
async def home():
    if client.isAuthenticated() is False:
        return "Not authenticated <a href='/sign-in'>Sign in</a>"
    return "Authenticated <a href='/sign-out'>Sign out</a>"

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 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 Python app. You should now be able to sign in with SMTP. Enjoy!

Create an application in Logto​

Integrate Flask with Logto​

Installation​

Init LogtoClient​

Implement sign-in and sign-out​

Handle authentication status​

Checkpoint: Test your application​

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​