In Laravel session is initialized in a middleware that is handled by this class:
\Illuminate\Session\Middleware\StartSession::class
When the service providers are booted, this middleware has not been executed, because all the middlewares execute after the service providers boot phase
So, instead of sharing the variable from a service provider, you can create a middleware and share the session variable from there, or you can use a view composer with a callback in your service provider:
public function boot()
{
view()->composer('*', function ($view)
{
//this code will be executed when the view is composed, so session will be available
$view->with('key', \Session::get('key') );
});
}
This will work, as the callback will be called before the views are composed, when the middleware has already been executed, so session will be availabe
In general, pay attention at your middleware's execution order: if you want to access the session from a middleware, that should execute after Laravel's StartSession::class
middleware