Have the user object contain an authorization object. Then, when the userobj wants to know if it's allowed to do certain things, it asks the authobj. The authobj replies with a boolean yes-or-no.

But then you have an ugly set of

sub method1 { 
    ...
    if ($self->authenticated) {
        ...
    } else {
        ...
    }
    ...
}

sub method2 { 
    ...
    if ($self->authenticated) {
        ...
    } else {
        ...
    }
    ...
}

sub method3 { 
    ...
    if ($self->authenticated) {
        ...
    } else {
        ...
    }
    ...
}
[download]

instead of a nice set of

package User::Anonymous;

sub method1 {
    ...
}

sub method2 {
    ...
}

sub method3 {
    ...
}

package User::Authenticated;

sub method1 {
    ...
}

sub method2 {
    ...
}

sub method3 {
    ...
}
[download]

I think checking inside the methods is (security) error prone, and a lot more work, resulting in uglier code that is harder to maintain. Besides that, it's less efficient because of the extra check (which if you abstract properly, is a method call). I prefer doing something that isn't entirely pure in the sense of "how OO was officially meant" (if such a thing even exists) to something that is pure, but causes me and the future maintenance guy extra work. And OO purity is a performance killer in many ways, which is a problem if you happen to work for one of those shops that still care about that.

So you can't easily subclass anymore. Fine with me, because you can still wrap. If I properly designed my User, I'd let you add arbitrary states like Anonymous and Authenticated, and you could change things through that interface. Personally, I don't think inheritance is holy enough to have as a primary design objective. Composition is more useful IMO, and reblessing to change state (combined with inheriting (or mixing in) from a state independent class) is a primitive way of doing that.