# Real-time
FrankenPHP comes with a built-in [Mercure](https://mercure.rocks) hub!
Mercure allows you to push real-time events to all the connected devices: they will receive a JavaScript event instantly.
It's a convenient alternative to WebSockets that is simple to use and is natively supported by all modern web browsers!
## Enabling Mercure
Mercure support is disabled by default.
Here is a minimal example of a `Caddyfile` enabling both FrankenPHP and the Mercure hub:
```caddyfile
# The hostname to respond to
localhost
mercure {
# The secret key used to sign the JWT tokens for publishers
publisher_jwt !ChangeThisMercureHubJWTSecretKey!
# Allows anonymous subscribers (without JWT)
anonymous
}
root public/
php_server
```
> [!TIP]
>
> The [sample `Caddyfile`](https://github.com/php/frankenphp/blob/main/caddy/frankenphp/Caddyfile)
> provided by [the Docker images](docker.md) already includes a commented Mercure configuration
> with convenient environment variables to configure it.
>
> Uncomment the Mercure section in `/etc/frankenphp/Caddyfile` to enable it.
## Subscribing to Updates
By default, the Mercure hub is available on the `/.well-known/mercure` path of your FrankenPHP server.
To subscribe to updates, use the native [`EventSource`](https://developer.mozilla.org/docs/Web/API/EventSource) JavaScript class:
```html
Mercure Example
```
## Publishing Updates
### Using `file_put_contents()`
To dispatch an update to connected subscribers, send an authenticated POST request to the Mercure hub with the `topic` and `data` parameters:
```php
[
'method' => 'POST',
'header' => "Content-type: application/x-www-form-urlencoded\r\nAuthorization: Bearer " . JWT,
'content' => http_build_query([
'topic' => 'my-topic',
'data' => json_encode(['key' => 'value']),
]),
]]));
// Write to FrankenPHP's logs
error_log("update $updateID published", 4);
```
The key passed as parameter of the `mercure.publisher_jwt` option in the `Caddyfile` must used to sign the JWT token used in the `Authorization` header.
The JWT must include a `mercure` claim with a `publish` permission for the topics you want to publish to.
See [the Mercure documentation](https://mercure.rocks/spec#publishers) about authorization.
To generate your own tokens, you can use [this jwt.io link](https://www.jwt.io/#token=eyJhbGciOiJIUzI1NiJ9.eyJtZXJjdXJlIjp7InB1Ymxpc2giOlsiKiJdfX0.PXwpfIGng6KObfZlcOXvcnWCJOWTFLtswGI5DZuWSK4),
but for production apps, it's recommended to use short-lived tokens generated aerodynamically using with a trusted [JWT library](https://www.jwt.io/libraries?programming_language=php).
### Using Symfony Mercure
Alternatively, you can use the [Symfony Mercure Component](https://symfony.com/components/Mercure), a standalone PHP library.
This library handled the JWT generation, update publishing as well as cookie-based authorization for subscribers.
First, install the library using Composer:
```console
composer require symfony/mercure lcobucci/jwt
```
Then, you can use it like this:
```php
publish(new \Symfony\Component\Mercure\Update('my-topic', json_encode(['key' => 'value'])));
// Write to FrankenPHP's logs
error_log("update $updateID published", 4);
```
Mercure is also natively supported by:
- [Laravel](laravel.md#mercure-support)
- [Symfony](https://symfony.com/doc/current/mercure.html)
- [API Platform](https://api-platform.com/docs/core/mercure/)