Middleware doesn't work with Broadcasting?

Trying to setup Broadcasting Authorization, but when I add the auth middleware in the BroadcastServiceProvider as such:

```php
Broadcast::routes([ 'middleware' => [ 'api.auth' ] ]);
```

It's throwing the following exception:

`Call to a member function getAuthenticationProviders() on a non-object`

Tried a few things, but can't get this to work. Any ideas?

Start with the BroadcastServiceProvider and the Broadcast::routes call shown in the report, then reproduce the failure using the api.auth middleware. Trace the getAuthenticationProviders exception and verify that broadcasting authorization works without the reported error when the issue is resolved.

Written by the indexing model from the issue text.