Um, its either done automatically (I hope) or you manipulate some object (transport?) :D I imagine http://perl.overmeer.net/xml-compile/#doc would have an example ... yeah use a transport "hook" http://perl.overmeer.net/xml-compile/html/XML_Compile_SOAP/index.html

 my $call = $wsdl->compileClient($operation
     , transport_hook => \&basic_auth );
  sub basic_auth($$)
  {   my ($request, $trace) = @_;

      # Encode userid and password
      my $authorization = 'Basic '. encode_base64 "$user:$password";

      # Modify http header to include basic authorisation
      $request->header(Authorization => $authorization );

      my $ua = $trace->{user_agent};
      $ua->request($request);
  }
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