Lucia

Tutorial: Username and password auth in Astro

Before starting, make sure you've set up your database and middleware as described in the Getting started page.

An example project based on this tutorial is also available. You can clone the example locally or open it in StackBlitz.

npx degit https://github.com/lucia-auth/examples/tree/main/astro/username-and-password <directory_name>

Update database

Add a username and hashed_password column to your user table.

column type attributes
username string unique
hashed_password string

Create a DatabaseUserAttributes interface in the module declaration and add your database columns. By default, Lucia will not expose any database columns to the User type. To add a username field to it, use the getUserAttributes() option.

import { Lucia } from "lucia";

export const lucia = new Lucia(adapter, {
	sessionCookie: {
		attributes: {
			secure: import.meta.env.PROD
		}
	},
	getUserAttributes: (attributes) => {
		return {
			// attributes has the type of DatabaseUserAttributes
			username: attributes.username
		};
	}
});

declare module "lucia" {
	interface Register {
		Lucia: typeof lucia;
		DatabaseUserAttributes: DatabaseUserAttributes;
	}
}

interface DatabaseUserAttributes {
	username: string;
}

Sign up user

Create pages/signup.astro and set up a basic form.

<!--pages/signup.astro-->
<html lang="en">
	<body>
		<h1>Sign up</h1>
		<form method="post" action="/api/signup">
			<label for="username">Username</label>
			<input id="username" name="username" />
			<label for="password">Password</label>
			<input id="password" name="password" />
			<button>Continue</button>
		</form>
	</body>
</html>

Create an API route in pages/api/signup.ts. First, do a very basic input validation. Hash the password, generate a new user ID, and create a new user. If successful, create a new session with Lucia.createSession() and set a new session cookie.

// pages/api/signup.ts
import { lucia } from "@lib/auth";
import { generateId } from "lucia";
import { Argon2id } from "oslo/password";

import type { APIContext } from "astro";

export async function POST(context: APIContext): Promise<Response> {
	const formData = await context.request.formData();
	const username = formData.get("username");
	// username must be between 4 ~ 31 characters, and only consists of lowercase letters, 0-9, -, and _
	// keep in mind some database (e.g. mysql) are case insensitive
	if (
		typeof username !== "string" ||
		username.length < 3 ||
		username.length > 31 ||
		!/^[a-z0-9_-]+$/.test(username)
	) {
		return new Response("Invalid username", {
			status: 400
		});
	}
	const password = formData.get("password");
	if (typeof password !== "string" || password.length < 6 || password.length > 255) {
		return new Response("Invalid password", {
			status: 400
		});
	}

	const userId = generateId(15);
	const hashedPassword = await new Argon2id().hash(password);

	// TODO: check if username is already used
	await db.table("user").insert({
		id: userId,
		username: username,
		hashed_password: hashedPassword
	});

	const session = await lucia.createSession(userId, {});
	const sessionCookie = lucia.createSessionCookie(session.id);
	context.cookies.set(sessionCookie.name, sessionCookie.value, sessionCookie.attributes);

	return context.redirect("/");
}

We recommend using Argon2id, but Oslo also provides Scrypt and Bcrypt. These only work in Node.js. If you're planning to deploy your project to a non-Node.js runtime, use Scrypt provided by lucia. This is a pure JS implementation but 2~3 times slower. For Bun, use Bun.password.

import { Scrypt } from "lucia";

new Scrypt().hash(password);

If you're using Bcrypt, set the maximum password length to 64 bytes.

const length = new TextEncoder().encode(password).length;

Sign in user

Create pages/login.astro and set up a basic form.

<!--pages/login.astro-->
<html lang="en">
	<body>
		<h1>Sign in</h1>
		<form method="post" action="/api/login">
			<label for="username">Username</label>
			<input id="username" name="username" />
			<label for="password">Password</label>
			<input id="password" name="password" />
			<button>Continue</button>
		</form>
	</body>
</html>

Create an API route as pages/api/signup.ts. First, do a very basic input validation. Get the user with the username and verify the password. If successful, create a new session with Lucia.createSession() and set a new session cookie.

// pages/api/login.ts
import { lucia } from "@lib/auth";
import { Argon2id } from "oslo/password";

import type { APIContext } from "astro";

export async function POST(context: APIContext): Promise<Response> {
	const formData = await context.request.formData();
	const username = formData.get("username");
	if (
		typeof username !== "string" ||
		username.length < 3 ||
		username.length > 31 ||
		!/^[a-z0-9_-]+$/.test(username)
	) {
		return new Response("Invalid username", {
			status: 400
		});
	}
	const password = formData.get("password");
	if (typeof password !== "string" || password.length < 6 || password.length > 255) {
		return new Response("Invalid password", {
			status: 400
		});
	}

	const existingUser = await db
		.table("username")
		.where("username", "=", username.toLowerCase())
		.get();
	if (!existingUser) {
		// NOTE:
		// Returning immediately allows malicious actors to figure out valid usernames from response times,
		// allowing them to only focus on guessing passwords in brute-force attacks.
		// As a preventive measure, you may want to hash passwords even for invalid usernames.
		// However, valid usernames can be already be revealed with the signup page among other methods.
		// It will also be much more resource intensive.
		// Since protecting against this is non-trivial,
		// it is crucial your implementation is protected against brute-force attacks with login throttling etc.
		// If usernames are public, you may outright tell the user that the username is invalid.
		return new Response("Incorrect username or password", {
			status: 400
		});
	}

	const validPassword = await new Argon2id().verify(existingUser.password, password);
	if (!validPassword) {
		return new Response("Incorrect username or password", {
			status: 400
		});
	}

	const session = await lucia.createSession(userId, {});
	const sessionCookie = lucia.createSessionCookie(session.id);
	context.cookies.set(sessionCookie.name, sessionCookie.value, sessionCookie.attributes);

	return context.redirect("/");
}

Validate requests

You can validate requests by checking locals.user. The field user.username is available since we defined the getUserAttributes() option. You can protect pages, such as /, by redirecting unauthenticated users to the login page.

const user = Astro.locals.user;
if (!user) {
	return Astro.redirect("/login");
}

const username = user.username;

Sign out

Sign out users by invalidating their session with Lucia.invalidateSession(). Make sure to remove their session cookie by setting a blank session cookie created with Lucia.createBlankSessionCookie().

import { lucia } from "@lib/auth";
import type { APIContext } from "astro";

export async function POST(context: APIContext): Promise<Response> {
	if (!context.locals.session) {
		return new Response(null, {
			status: 401
		});
	}

	await lucia.invalidateSession(context.locals.session.id);

	const sessionCookie = lucia.createBlankSessionCookie();
	context.cookies.set(sessionCookie.name, sessionCookie.value, sessionCookie.attributes);

	return Astro.redirect("/login");
}
<form method="post" action="/api/logout">
	<button>Sign out</button>
</form>