Getting PropertyAttribute from PropertyDrawer.OnGUI

Hi guys

I've written a custom PropertyAttribute class and I want to use a custom PropertyDrawer class to access and display data on the PropertyAttribute.

So far I have something like this:

 [Serializable]
 public class CustomPropertyAttribute : PropertyAttribute
 {
     public A a {get; set;}
     public B b {get; set;}
 }
 
 [CustomPropertyDrawer(typeof(CustomPropertyAttribute))]
 public class CustomPropertyDrawer : PropertyDrawer
 {
     public override void OnGUI(Rect position, SerializedProperty prop,
                                GUIContent label)
     {
         // How do I access the CustomPropertyAttribute properties here?
     }
 }

How can I get at the CustomPropertyAttribute from inside the OnGUI method?

The documentation suggests using the "attribute" property:

But then says it isn't applicable with custom drawers (it returns null when I try it), so I fail to see when it would ever be useful.

I've also tried:

 prop.serializedObject as CustomPropertyAttribute;

But the compiler isn't happy with the conversion.

Can anyone please explain how I can use the PropertyDrawer effectively?