Authorisation - proving who you are 

• collect certain parts of the request:

• e.g. headers and/or parameter values

use Digest::HMAC_SHA1;
my @order = sort { lc($a) cmp lc($b) } keys %$request;
my $data = reduce { $a . $b . $request->{$b} } '', @order;
my $digest = Digest::HMAC_SHA1->new( $self->secret_access_key );
$digest->add( $data );

• DomainNamemydomainActionQueryDateMon 10 Jan 2008....

• include the signature in the request