Send the Authorization header with every request. You don't have to wait for the server to challenge you (and for those of you who think that, recall that HTTP is a stateless protocol). From RFC 2616, Section 14.8 (I added the emphasis):

A user agent that wishes to authenticate itself with a server--usually, but not necessarily, after receiving a 401 response--does so by including an Authorization request-header field with the request.

You don't have to force LWP to do it; it sounds like the ATOM client needs to know to do it.

It's difficult to point to any concrete fixes without code though.

Update: added the extract from RFC 2616

Thanks for the replies so far. In my case, I'm using RT::Client (not sure if it's on CPAN - I think $work paid Best Practical to write it). It uses a custom LWP UserAgent class so it (hopefully) should be straightforward to add a header on outgoing requests. Now I just need to dive into LWP to figure out how to set headers.

my $rv = $self->SUPER::new(%args);
$rv->ua( LWP::UserAgent::RTClient->new($rv) );
$rv->ua->{keep_alive} = 1;
$rv->ua->{requests_redirectable} = [ qw( GET HEAD OPTIONS ) ];
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Thanks,
Drew

But if you know realm and authentication mechanism, you could try to add an appropriate "Authorization:" header directly to the HTTP::Headers structure of the LWP object; don't know whether that works (i.e. whether LWP ignores that header line on the initial request and behaves standard anyways), but it could be worth a try.

--shmem

_($_=" "x(1<<5)."?\n".q·/)Oo.  G°\        /
                              /\_¯/(q    /
----------------------------  \__(m.====·.(_("always off the crowd"))."·
");sub _{s./.($e="'Itrs `mnsgdq Gdbj O`qkdq")=~y/"-y/#-z/;$e.e && print}

But for reference in case anyone needs it, here's what I added to RT/Client.pm. X-WSSE and Authentication are definitely required. I couldn't quickly determine if the WWW-Authenticate header is required by the spec so I sent it along anyway (after trying it both ways).

my ($username, $password) = $ua->get_basic_credentials("Support");
# This code is culled from XML::Atom::Client::munge_request().
my $nonce = XML::Atom::Client::make_nonce();                          
+     
my $nonce_enc = encode_base64($nonce, '');                            
+     
my $now = DateTime->now->iso8601 . 'Z';                               
+     
my $digest = encode_base64(sha1($nonce . $now . ($password || '')), ''
+);
$ua->default_header('WWW-Authenticate', 'WSSE realm="Support", profile
+="UsernameToken"');                                                  
+               
$ua->default_header('Authorization', 'WSSE profile="UsernameToken"');
$ua->default_header('X-WSSE', sprintf                                 
+     
                 qq(UsernameToken Username="%s", PasswordDigest="%s", 
+Nonce="%s", Created="%s"),                                           
+               
             $username || '', $digest, $nonce_enc, $now);
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