accessing https URLS with basic authentification

[Ben Rubinstein]

I can load an "https" URL fine.

I can load an "http" URL protected using 'basic' authentification, using 
either the "http://user:password@www.somewhere.com/" format, or by using the 
HTTPHeaders property to explicitly add an "Authorization: Basic xxx" header.

But I can't load an "https" URL that's protected using basic authentification, 
using either of the methods described above.

Is this a known problem?  Can anyone else either reproduce this problem, or 
alternatively confirm that they _can_ load such a URL?

(NB1 this is on Mac OS X, Rev 3.0 and 3.5.)

(NB2 I can retrieve the URL fine using "curl" in the terminal - and in fact 
for now I'm working around the problem by using shell() to invoke curl.  But I 
really want to handle URLs of this form in the same way I'm handling other 
http URLs in my app, which give me more control.)

Any insights gratefully received,

TIA

Ben