Sk Auth

Authentication library for use with SvelteKit featuring built-in OAuth providers and zero restriction customization!


Authentication library for use with SvelteKit featuring built-in OAuth providers and zero restriction customization!


SvelteKitAuth is available on NPM as sk-auth, it can be installed with NPM:

npm i sk-auth --save

Or Yarn:

yarn add sk-auth

Usage with Typescript

SvelteKitAuth also comes with first-class support for Typescript out of the box, so no need to add an additional @types/ dev dependency! šŸŽ‰

Getting Started

SvelteKitAuth is very easy to setup! All you need to do is instantiate the SvelteKitAuth class, and configure it with some default providers, as well as a JWT secret key used to verify the cookies:

Warning: env variables prefixed with VITE_ can be exposed and leaked into client-side bundles if they are referenced in any client-side code. Make sure this is not the case, or consider using an alternative method such as loading them via dotenv directly instead.

export const appAuth = new SvelteKitAuth({
  providers: [
    new GoogleOAuthProvider({
      clientId: import.meta.env.VITE_GOOGLE_OAUTH_CLIENT_ID,
      clientSecret: import.meta.env.VITE_GOOGLE_OAUTH_CLIENT_SECRET,
      profile(profile) {
        return { ...profile, provider: "google" };
  jwtSecret: import.meta.env.JWT_SECRET_KEY,

If you want to override or augment the default SvelteKit session to get access to the user in the session store, you can use the getSession hook:

// overriding the default session
export const { getSession } = appAuth;

// augmenting it
export const getSession: GetSession = async (request) => {
  const { user } = await appAuth.getSession(request);

  return { user };


SvelteKitAuth provides some callbacks, similar to NextAuth.js. Their call signatures are:

interface AuthCallbacks {
  signIn?: () => boolean | Promise<boolean>;
  jwt?: (token: JWT, profile?: any) => JWT | Promise<JWT>;
  session?: (token: JWT, session: Session) => Session | Promise<Session>;
  redirect?: (url: string) => string | Promise<string>;

Adding more Providers

SvelteKitAuth uses a object-oriented approach towards creating providers. It is unopionated and allows you to implement any three-legged authentication flow such as OAuth, SAML SSO, and even regular credential logins by omitting the signin() route.

You can implement your own using the Provider base provider class, and by implementing the signin() and callback() methods:

export abstract class Provider<T extends ProviderConfig = ProviderConfig> {
  abstract signin<Locals extends Record<string, any> = Record<string, any>, Body = unknown>(
    request: ServerRequest<Locals, Body>,
  ): EndpointOutput | Promise<EndpointOutput>;

  abstract callback<Locals extends Record<string, any> = Record<string, any>, Body = unknown>(
    request: ServerRequest<Locals, Body>,
  ): CallbackResult | Promise<CallbackResult>;

signin() must return a generic endpoint output, this can be a redirect, or the path to the provider's sign-in page. When implementing a HTTP POST route, signin() can simply return an empty body and callback() should handle the user login flow.

callback() takes a ServerRequest and must return a CallbackResult which is a custom type exported by svelte-kit-auth:

export type Profile = any;
export type CallbackResult = [Profile, string | null];

The first item in the tuple is the user profile, which gets stored in the token, and is provided to the jwt() callback as the second argument. The second item is a redirect route, which may be tracked using the state query parameter for OAuth providers, or other implementations depending on the sign-in method.


SvelteKitAuth comes with a built-in OAuth2 provider that takes extensive configuration parameters to support almost any common OAuth2 provider which follows the OAuth2 spec. It can be imported from sk-auth/providers and configured with the following configuration object:

export interface OAuth2ProviderConfig<ProfileType = any, TokensType extends OAuth2Tokens = any>
  extends OAuth2BaseProviderConfig<ProfileType, TokensType> {
  accessTokenUrl?: string;
  authorizationUrl?: string;
  profileUrl?: string;
  clientId?: string;
  clientSecret?: string;
  scope: string | string[];
  headers?: any;
  authorizationParams?: any;
  params: any;
  grantType?: string;
  responseType?: string;
  contentType?: "application/json" | "application/x-www-form-urlencoded";

Some values have defaults which can be seen below:

const defaultConfig: Partial<OAuth2ProviderConfig> = {
  responseType: "code",
  grantType: "authorization_code",
  contentType: "application/json",

The OAuth2Provider class can then be instantiated with the configuration to support the OAuth2 flow, including authorization redirect, token retrieval and profile fetching. It will also automatically handle the state and nonce params for you.


SvelteKitAuth is inspired by the NextAuth.js package built for the Next.js SSR framework for React. Unlike NextAuth.js it is completely unopinionated and only provides implementations for default flows, while still empowering users to add their own providers.

As it leverages classes and Typescript, the implementation of such providers is very straightforward, and in the future it will even be possible to register multiple SvelteKitAuth handlers in the same project, should the need arise, by leveraging a class-based client and server setup.


Looking for help? Check out the example app in the repository source. Make something cool you want to show off? Share it with others in the discussion section.


šŸš§ Work in Progress!


This project is licensed under the terms of the MIT license.

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