Passing as parameter a generic type in an attribute in . NET MVC

Question

In another question I asked here I had to modify my authentication class to return the values of the model referring to the user and the authenticated user type, for example, admins, users, clients, so I had to implement a generic type to the call, and a new interface. But in conjunction with the authentication class I use a ActionFilterAttribute to allow or deny access to Routes, the statement is:

[Authorized("users")]
public ActionResult Index()
{
    ...

But because it’s an attribute I’m not able to implement a generic type so I can use the authentication class to do the necessary checks, as in the following example, which doesn’t work, but is only to describe the need:

Statement:

[Authorized<users>]
public ActionResult Index()
{
    ...

Filter:

public class Authorized : ActionFilterAttribute
{
    private T guard;

    public Authorized<T>() where T : class, IAuth
    {
        this.guard = guard;
    }

    public override void OnActionExecuting(ActionExecutingContext filterContext)
    {
        if(Auth.<T>Check())
            ...
    }
}

So I tried to start the type through a string like in the first example, the filter class is:

public class Authorized : ActionFilterAttribute
{
    private string guard_name;

    public Authorized(string guard_name)
    {
        this.guard_name = guard_name;
    }

    public override void OnActionExecuting(ActionExecutingContext filterContext)
    {
        if(Auth.Guard(guard_name).Check())
            ...
    }
}

Notice that in the execution I do the verification with the method Check() which receives as parameter T the return of the method Guard(), that takes a string and returns a type.

Auth.Guard(string guard_name).Check()

The method Guard class Auth gets like this:

public static T Guard<T>(string guard_name) where T : class, IAuth
{
    return (T)Activator.CreateInstance(Type.GetType(guard_name));
}

And it didn’t work either because the method Auth.Guard() not only accepts a string, it is necessary to also be passed as reference a type to pass as T parameter for other methods like Auth.Check(), but inside the filter Autorized I have no way to pass this reference.

I tried this way and it doesn’t work either because the T is invalid:

public static T Guard(string guard_name)
{
    return (T)Activator.CreateInstance(Type.GetType(guard_name));
}

How can I solve?

Answer 1

You can pass a type to your attribute:

[Authorized(typeof(User))]

Your attribute would have to change a little:

public class Authorized : ActionFilterAttribute
{
    private Type guardType;

    ...
}

The call to the verification method I would do as follows:

public override void OnActionExecuting(ActionExecutingContext filterContext)
{
    if(Auth.Check(guardType))
        ...
}

Check must have a signature like this:

public bool Check(Type tipo) { ... }