WPF permission-based authorization using Enum Flag

Question

I've been doing C# for a month now so please forgive the 'localness' to this question but I have researched for a few hours and I have hit a brick wall.

I've seen examples left and right for Role-based authorization for WPF applications utilizing IIdentity and IPrincipal.

I can't find a lot of information, however, on a more Permission-based authorization approach, in this app imagine there are no Groups but just a list of permissions and users and you can assign anyone any permission.

I'd like to be able to:

1) Be able to control the UI/elements based on user permissions with such states as: Enabled, ReadOnly, Invisible, Collapsed (as seen here https://uiauth.codeplex.com/)
2) Be able to specify at the class or method level which permissions are required (similar to http://lostechies.com/derickbailey/2011/05/24/dont-do-role-based-authorization-checks-do-activity-based-checks/)

Instead of:

[PrincipalPermission(SecurityAction.Demand, Role = "Administrators")]

I want something like:

[PrincipalPermission(SecurityAction.Demand, Permission = "Can add users")]

Right now the only way I see how to do this is utilizing ICommand and putting authorization logic in the CanExecute methods using a lot of string comparison to see if the user has the required rights to perform requested actions like:

// Employee class
public bool HasRight(SecurityRight right)
{
    return employee.Permissions.Contains(right);
}

// Implementation, check if employee has right to continue
if (employee.HasRight(db.SecurityRights.Single(sr => sr.Description == "Can edit users")))
{
    // Allowed to perform action
}
else
{
    // User does not have right to continue
    throw SecurityException;
}

I've been told Enum Flags may be what I'm looking for What does the [Flags] Enum Attribute mean in C#?

I think I understand enum/flag/bits but not enough to complete the implementation...

If I have:

EmployeeModel
EmployeeViewModel
ThingTwoModel
ThingTwoViewModel
MainView

I'm not sure where everything goes and how to tie it all together.... here's what I have so far (I realize this isnt a working example... thats my problem!):

    [Flags]
    public enum Permissions
    {
        None = 0,
        Create = 1 << 0,
        Read = 1 << 1,
        Update = 1 << 2,
        Delete = 1 << 3,

        User = 1 << 4,
        Group = 1 << 5
    }

    public static void testFlag()
    {
        Permissions p;
        var x = p.HasFlag(Permissions.Update) && p.HasFlag(Permissions.User);
        var desiredPermissions = Permissions.User | Permissions.Read | Permissions.Create;
        if (x & p == desiredPermissions)
        {
            //the user can be created and read by this operator
        }
    }

Thank you for any guidance.

Answer 1

Final solution (.linq):

void Main()
{
    // Permissions definition
    var userCreate = new Authorization<User>(Permissions.Create);
    var userRead = new Authorization<User>(Permissions.Read);

    var carrotCreate = new Authorization<Carrot>(Permissions.Create);
    var carrotRead = new Authorization<Carrot>(Permissions.Read);

    // User
    var user = new User();

    // User has no permissions yet
    if(user.IsAuthorized<User>(Permissions.Create))
        "I can create User".Dump();
    else
        "No creating User for me".Dump();

    // Now user can Create users
    user.Authorizations.Add(userCreate);            
    if(user.IsAuthorized<User>(Permissions.Create))
        "I can create User".Dump();
    else
        "No creating User for me".Dump();

    // User can read carrots
    user.Authorizations.Add(carrotRead);

    if(user.IsAuthorized<Carrot>(Permissions.Create))
        "I can create carrots".Dump();
    else
        "No creating carrots for me".Dump();

    if(user.IsAuthorized<Carrot>(Permissions.Read))
        "I can read carrots".Dump();
    else
        "No reading carrots for me".Dump();

    // User can now create carrots
    user.Authorizations.Add(carrotCreate);
    if(user.IsAuthorized<Carrot>(Permissions.Create))
        "I can create carrots".Dump();
    else
        "No creating carrots for me".Dump();            

}

[Flags]
public enum Permissions : ulong
{
    Create = 1 << 0,
    Read = 1 << 1,
    Update = 1 << 2,
    Delete = 1 << 3
}

public abstract class Auth{

}
public class Authorization<T> : Auth {
    public Authorization(Permissions permissions){ this.Permissions = permissions; }
    public Permissions Permissions {get;set;}
}

public class Carrot{
    public int Id{get; set;}
}

public class User{
    public User(){ Authorizations = new List<Auth>(); }
    public List<Auth> Authorizations{get; set;}
    public bool IsAuthorized<T>(Permissions permission){
        foreach(var auth in Authorizations)
            if(auth is Authorization<T>){
                var a = auth as Authorization<T>;
                if(a.Permissions == permission)
                    return true;
            }

        return false;
    }
}

Answer 2

well the testFlag won't work as it is. I think you want something along the lines of (LINQPad c# program snippet):

void Main()
{
    //can create user but not read the information back
    var userCanBeCreatedPermission = Permissions.Create | Permissions.User;

    //can create and readback
    var userCanBeCreatedAndReadBackPermission = userCanBeCreatedPermission | Permissions.Read;

    userCanBeCreatedPermission.HasFlag(Permissions.User).Dump(); //returns true

    (userCanBeCreatedPermission.HasFlag(Permissions.User) && userCanBeCreatedPermission.HasFlag(Permissions.Read)).Dump(); //returns false

    //alternative way of checking flags is to combine the flags and do an And mask check
    //the above can be written as
    ((userCanBeCreatedPermission & (Permissions.User | Permissions.Read)) == (Permissions.User | Permissions.Read)).Dump(); //returns false

    //using a variable to have combined permissions for readibility & using And mask:
    var desiredPermissions = Permissions.User | Permissions.Read;

    //checking with user that has both Create & Read permissions

    ((userCanBeCreatedAndReadBackPermission & desiredPermissions) == desiredPermissions).Dump(); // returns true because the user information can be read back by this user

    ((userCanBeCreatedAndReadBackPermission & Permissions.Delete) == Permissions.Delete).Dump(); // returns false because the user can't be deleted
}

[Flags]
public enum Permissions
{
   None = 0,
   Create = 1 << 0,
   Read = 1 << 1,
   Update = 1 << 2,
   Delete = 1 << 3,

   User = 1 << 4,
   Group = 1 << 5
}

Does that answer your question?