Are you saying I'm imagining that it works?

# for debugging
#my $outfile = "out.htm";
#my $output_page = $mech->content();
#open(OUTFILE, ">$outfile");
#print OUTFILE "$output_page";
# end debug
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I save the content into a file. And I examine the file and sure enough I get the page after the login page. So the form is POSTing.