# Clerk Fastify SDK

The Clerk Fastify SDK provides a powerful set of tools and utilities to seamlessly integrate authentication, user management, and Organization management into your Fastify application. Refer to the [quickstart guide](https://clerk.com/docs/fastify/getting-started/quickstart.md) to get started.

## `clerkPlugin()`

The `clerkPlugin()` function is required to integrate Clerk's authentication into your application. The function checks request cookies and headers for a session JWT. If valid, it attaches the [`Auth`](https://clerk.com/docs/reference/backend/types/auth-object.md){{ target: '_blank' }} object to the `request` object under the `auth` key. See the [reference doc](https://clerk.com/docs/reference/fastify/clerk-plugin.md) for more information.

## `getAuth()`

The `getAuth()` helper retrieves the current user's authentication state from the `request` object. It returns the [`Auth` object](https://clerk.com/docs/reference/backend/types/auth-object.md){{ target: '_blank' }}, which includes helpful authentication information like the user's ID, session ID, and Organization ID. It's also useful for protecting routes. See the [reference doc](https://clerk.com/docs/reference/fastify/get-auth.md) for more information.

## `clerkClient`

[`clerkClient`](https://clerk.com/docs/reference/backend/overview.md) is a wrapper around the [Backend API](https://clerk.com/docs/reference/backend-api){{ target: '_blank' }} that makes it easier to interact with the API. For example, to retrieve a list of all users in your application, you can use the `users.getUserList()` method instead of manually making a fetch request to the `https://api.clerk.com/v1/users` endpoint.

To access a resource, you must first instantiate a `clerkClient` instance. See the [reference documentation](https://clerk.com/docs/reference/backend/overview.md) for more information.

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