I tried the method you have specified to use:

however, it does not work either and gives the same error:

"The authorization type you provided is not supported. Only Basic and OAuth are supported".

I have even tried specifying a valid user agent, just in case they are performing User Agent Sniffing and it does not work.

So, I set the user agent alias as follows:

$mech->agent_alias('Windows IE 6');

Again, I receive the same error for authentication.