Tutorial: Username and password auth in SvelteKit

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/v3/sveltekit/username-and-password

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";
import { dev } from "$app/environment";

export const lucia = new Lucia(adapter, {
	sessionCookie: {
		attributes: {
			secure: !dev
		}
	},
	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;
}

Create routes/signup/+page.svelte and set up a basic form.

<!-- routes/signup/+page.svelte -->
<script lang="ts">
	import { enhance } from "$app/forms";
</script>

<h1>Sign up</h1>
<form method="post" use:enhance>
	<label for="username">Username</label>
	<input name="username" id="username" /><br />
	<label for="password">Password</label>
	<input type="password" name="password" id="password" /><br />
    <button>Continue</button>
</form>

Create a form action in routes/signup/+page.server.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.

// routes/signup/+page.server.ts
import { lucia } from "$lib/server/auth";
import { fail, redirect } from "@sveltejs/kit";
import { Argon2id } from "oslo/password";

import type { Actions } from "./$types";

export const actions: Actions = {
	default: async (event) => {
		const formData = await event.request.formData();
		const username = formData.get("username");
		const password = formData.get("password");
		// 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 fail(400, {
				message: "Invalid username"
			});
		}
		if (typeof password !== "string" || password.length < 6 || password.length > 255) {
			return fail(400, {
				message: "Invalid password"
			});
		}

		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);
		event.cookies.set(sessionCookie.name, sessionCookie.value, {
			path: ".",
			...sessionCookie.attributes
		});

		redirect(302, "/");
	}
};

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;

Create routes/login/+page.svelte and set up a basic form.

<!-- routes/login/+page.svelte -->
<script lang="ts">
	import { enhance } from "$app/forms";
</script>

<h1>Sign in</h1>
<form method="post" use:enhance>
	<label for="username">Username</label>
	<input name="username" id="username" /><br />
	<label for="password">Password</label>
	<input type="password" name="password" id="password" /><br />
	<button>Continue</button>
</form>

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.

import { lucia } from "$lib/server/auth";
import { fail, redirect } from "@sveltejs/kit";
import { Argon2id } from "oslo/password";

import type { Actions } from "./$types";

export const actions: Actions = {
	default: async (event) => {
		const formData = await event.request.formData();
		const username = formData.get("username");
		const password = formData.get("password");

		if (
			typeof username !== "string" ||
			username.length < 3 ||
			username.length > 31 ||
			!/^[a-z0-9_-]+$/.test(username)
		) {
			return fail(400, {
				message: "Invalid username"
			});
		}
		if (typeof password !== "string" || password.length < 6 || password.length > 255) {
			return fail(400, {
				message: "Invalid password"
			});
		}

		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 none-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 fail(400, {
				message: "Incorrect username or password"
			});
		}

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

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

		redirect(302, "/");
	}
};

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.

// +page.server.ts
import type { PageServerLoad, Actions } from "./$types";

export const load: PageServerLoad = async (event) => {
	if (!event.locals.user) redirect(302, "/login");
	return {
		username: event.locals.user.username
	};
};

Sign out user

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().

// routes/+page.server.ts
import { lucia } from "$lib/server/auth";
import { fail, redirect } from "@sveltejs/kit";

import type { Actions, PageServerLoad } from "./$types";

export const load: PageServerLoad = async ({ locals }) => {
	// ...
};

export const actions: Actions = {
	default: async (event) => {
		if (!event.locals.session) {
			return fail(401);
		}
		await auth.invalidateSession(event.locals.session.id);
		const sessionCookie = lucia.createBlankSessionCookie();
		event.cookies.set(sessionCookie.name, sessionCookie.value, {
			path: ".",
			...sessionCookie.attributes
		});
		redirect(302, "/login");
	}
};

<!-- routes/+page.svelte -->
<script lang="ts">
	import { enhance } from "$app/forms";
</script>

<form method="post" use:enhance>
    <button>Sign out</button>
</form>

Tutorial: Username and password auth in SvelteKit

Update database

Sign up user

Sign in user

Validate requests

Sign out user