Ok finally I found it out how to get the ISchoolyearService from the current request:
Grab the registered service from the DependencyScope!
Now this Attribute should be put on the controller directly. Its not needed to put it on the action due to the if/else on the http verbs which I do.
bool canUserExecuteAction = false;
if (actionContext.Request.Method == HttpMethod.Put)
{
int targetId = Convert.ToInt32(actionContext.Request.GetRouteData().Values["Id"]);
int userId = actionContext.Request.Content.ReadAsAsync<SchoolyearEditRequest>().Result.Schoolyear.UserId;
var requstScope = actionContext.ControllerContext.Request.GetDependencyScope();
var service = requstScope.GetService(typeof(ISchoolyearService)) as ISchoolyearService;
canUserExecuteAction = service.HasUserPermission(userId, targetId);
if (canUserExecuteAction)
{
base.OnAuthorization(actionContext);
}
else
{
actionContext.Response = new HttpResponseMessage(HttpStatusCode.Forbidden);
}
}