supabase/apps/reference/docs/guides/auth/server-side-rendering.mdx

---
id: server-side-rendering
title: Server-Side Rendering
description: Render pages with user information on the server.
---

Single-page apps with server-side rendering (SSR) is a popular way to optimize rendering
performance and leverage advanced caching strategies.

Supabase Auth supports server-side rendering when you need access to user
information, or your server needs to authorize API requests on behalf of your
user to render content.

When a user authenticates with Supabase Auth, two pieces of information are
issued by the server:

1. **Access token** in the form of a JWT.
2. **Refresh token** which is a randomly generated string.

Most Supabase projects have their auth server listening on
`<project-ref>.supabase.co/auth/v1`, thus the access token and refresh token are
set as `sb-access-token` and `sb-refresh-token` cookies on the
`<project-ref>.supabase.co` domain.

:::note
These cookie names are for internal Supabase use only and may change without
warning. They are included in this guide for illustration purposes only.
:::

Web browsers limit access to cookies across domains, consistent with the
[Same-Origin Policy
(SOP)](https://developer.mozilla.org/en-US/docs/Web/Security/Same-origin_policy).

Your web application cannot access these cookies,
nor will these cookies be sent to your application's server.

## Understanding the authentication flow

When you call one of the `signIn` methods, the client library running in the
browser sends the request to the Supabase Auth server. The Auth server determines
whether to verify a phone number, email and password combination, a Magic Link,
or use a social login (if you have any setup in your project).

Upon successful verification of the identity of the user, the Supabase Auth
server redirects the user back to your single-page app.

:::tip
You can configure [redirects URLs](https://app.supabase.com/project/_/auth/settings) in the Supabase Dashboard. You can use wildcard match patterns
like `*` and `**` to allow redirects to different forms of URLs.
:::

These redirect URLs have the following structure:

```
https://yourapp.com/...#access_token=<...>&refresh_token=<...>&...
```

The first access and refresh tokens after a successful verification are
contained in the URL fragment (anything after the `#` sign) of the redirect
location. This is intentional and not configurable.

The client libraries are designed to listen for this type of URL, extract
the access token, refresh token and some extra information from it, and finally
persist it in local storage for further use by the library and your app.

:::info
Web browsers do not send the URL fragment to the server they're making the
request to. Since you may not be hosting the single-page app on a server under
your direct control (such as on GitHub Pages or other freemium hosting
providers), we want to prevent hosting services from getting access to your
user's authorization credentials by default. Even if the server is under your
direct control, `GET` requests and their full URLs are often logged. This
approach also avoids leaking credentials in request or access logs.
:::

## Bringing it together

As seen from the authentication flow, the initial request after successful
login made by the browser to your app's server after user login **does not
contain any information about the user**. This is because first the client-side
JavaScript library must run before it makes the access and refresh token
available to your server.

It is very important to make sure that the redirect route right after login
works without any server-side rendering. Other routes requiring authorization
do not have the same limitation, provided you send the access and refresh
tokens to your server.

This is traditionally done by setting cookies. Here's an example you
can add to the root of your application:

```typescript
supabase.auth.onAuthStateChange((event, session) => {
  if (event === "SIGNED_OUT" || event === "USER_DELETED") {
    // delete cookies on sign out
    const expires = new Date(0).toUTCString();
    document.cookie = `my-access-token=; path=/; expires=${expires}; SameSite=Lax; secure`;
    document.cookie = `my-refresh-token=; path=/; expires=${expires}; SameSite=Lax; secure`;
  } else if (event === "SIGNED_IN" || event === "TOKEN_REFRESHED") {
    const maxAge = 100 * 365 * 24 * 60 * 60; // 100 years, never expires
    document.cookie = `my-access-token=${session.access_token}; path=/; max-age=${maxAge}; SameSite=Lax; secure`;
    document.cookie = `my-refresh-token=${session.refresh_token}; path=/; max-age=${maxAge}; SameSite=Lax; secure`;
  }
})
```

This uses the standard
[`document.cookie` API](https://developer.mozilla.org/en-US/docs/Web/API/Document/cookie)
to set cookies on all paths of your app's domain. All subsequent requests
made by the browser to your app's server include the `my-access-token` and
`my-refresh-token` cookies (the names of the cookies and additional
parameters can be changed).

In your server-side rendering code you can now access user and session
information:


```typescript
const refreshToken = req.cookies['my-refresh-token'];
const accessToken = req.cookies['my-access-token'];

if (refreshToken && accessToken) {
  await supabase.auth.setSession({
    refresh_token: refreshToken,
    access_token: accessToken 
  });
} else {
  // make sure you handle this case!
  throw new Error("User is not authenticated.")
}

// returns user information
await supabase.auth.getUser();
```

Use `setSession({ access_token, refresh_token })` instead of
`setSession(refreshToken)` or `getUser(accessToken)` as refresh tokens or access tokens alone do not properly identify a user session. 

Access tokens are valid only for a short amount of time.

Even though refresh tokens are long-lived, there is no guarantee that a user
has an active session. They may have logged out and your application failed to
remove the `my-refresh-token` cookie, or some other failure occurred that left
a stale refresh token in the browser. Furthermore, a refresh token can only be
used a few seconds after it was first used. Only use a refresh token if the
access token is about to expire, which will avoid the introduction of difficult
to diagnose logout bugs in your app.

A good practice is to handle unauthorized errors by deferring rendering the
page in the browser instead of in the server. Some user information is
contained in the access token though, so in certain cases, you may be able to
use this potentially stale information to render a page.

## Frequently Asked Questions

### How do I make the cookies `HttpOnly`?

This is not necessary. Both the access token and refresh token are designed to
be passed around to different components in your application. The browser-based
side of your application needs access to the refresh token to properly maintain
a browser session anyway.

### My server is getting invalid refresh token errors. What's going on?

It is likely that the refresh token sent from the browser to your server is
stale. Make sure the `onAuthStateChange` listener callback is free of bugs and
is registered relatively early in your application's lifetime.

When you receive this error on the server-side, try to defer
rendering to the browser where the client library can access an up-to-date
refresh token and present the user with a better experience.

### Should I set a shorter `Max-Age` parameter on the cookies?

The `Max-Age` or `Expires` cookie parameters only control whether the browser
sends the value to the server. Since a refresh token represents the
long-lived authentication session of the user on that browser, setting a short
`Max-Age` or `Expires` parameter on the cookies only results in a degraded
user experience.

The only way to ensure that a user has logged out or their session has ended
is to get the user's details with `getUser()`.

### What should I use for the `SameSite` property?

Make sure you [understand the behavior of the property in different
situations](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Set-Cookie/SameSite)
as some properties can degrade the user experience.

A good default is to use `Lax` which sends cookies when users are
navigating to your site. Cookies typically require the `Secure` attribute,
which only sends them over HTTPS. However, this can be a problem when
developing on `localhost`.

### Can I use server-side rendering with a CDN or cache?

Yes, but you need to be careful to include at least the refresh token cookie
value in the cache key. Otherwise you may be accidentally serving pages with
data belonging to different users!

Also be sure you set proper cache control headers. We recommend invalidating
cache keys every hour or less.