You can set configuration values at runtime by passing an array to the config helper:
config(['imagecache.paths' => [
public_path('image/'.Auth::user()->username),
public_path('image')
]
]);
And to set it in every request, you can do this in a service provider. Add the following code in your boot method of App\Providers\AppServiceProvider class:
public function boot()
{
if (auth()->check()) {
config(['imagecache.paths' => [
public_path('image/'.Auth::user()->username),
public_path('image')
]
]);
}
}