I have another issue I am trying to iron out and in the process of trying to simplify the issue I've created the most simple UmbracoAuthorizedJsonController implementation as follows:

[PluginController("MyPlugIn")]
public class DataMigratorController : UmbracoAuthorizedJsonController
{
    [HttpGet]
    public object HelloWorld()
    {
        return new { Message = "Hello World" };
    }
}

If I browse to /umbraco/backoffice/Myplugin/DataMigrator/HelloWorld before login I get the expected 401 Unauthorized - great, that's what I want! However, when I login to Umbraco and then load the same path I get a 417 Missing token error returned. I've read numerous posts on here about deleting cookies, clearing cache and incrementing the ClientDependency version number and none have helped.

Not sure where to go from here?

Umbraco v7.5.8