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package AWS::Signature4;

use strict;
use POSIX 'strftime';
use URI;
use URI::QueryParam;
use URI::Escape;
use Digest::SHA 'sha256_hex','hmac_sha256','hmac_sha256_hex';
use Date::Parse;
use Carp 'croak';

our $VERSION = '1.02';

=head1 NAME

AWS::Signature4 - Create a version4 signature for Amazon Web Services

=head1 SYNOPSIS

 use AWS::Signature4;
 use HTTP::Request::Common;
 use LWP;

 my $signer = AWS::Signature4->new(-access_key => 'AKIDEXAMPLE',
                                   -secret_key => 'wJalrXUtnFEMI/K7MDENG+bPxRfiCYEXAMPLEKEY');
 my $ua     = LWP::UserAgent->new();

 # Example POST request
 my $request = POST('https://iam.amazonaws.com',
		    [Action=>'ListUsers',
		     Version=>'2010-05-08']);
 $signer->sign($request);
 my $response = $ua->request($request);

 # Example GET request
 my $uri     = URI->new('https://iam.amazonaws.com');
 $uri->query_form(Action=>'ListUsers',
		  Version=>'2010-05-08');

 my $url = $signer->signed_url($uri); # This gives a signed URL that can be fetched by a browser
 my $response = $ua->get($url);

=head1 DESCRIPTION

This module implement's Amazon Web Service's Signature version 4
(http://docs.aws.amazon.com/general/latest/gr/signature-version-4.html).

=head1 METHODS

=over 4

=item $signer = AWS::Signature4->new(-access_key => $account_id,-secret_key => $private_key);

Create a signing object using your AWS account ID and secret key. You
may also use the temporary security tokens received from Amazon's STS
service, either by passing the access and secret keys derived from the
token, or by passing a VM::EC2::Security::Token produced by the
VM::EC2 module.

Arguments:

 Argument name       Argument Value
 -------------       --------------
 -access_key         An AWS acccess key (account ID)

 -secret_key         An AWS secret key

 -security_token     A VM::EC2::Security::Token object


If a security token is provided, it overrides any values given for
-access_key or -secret_key.

If the environment variables EC2_ACCESS_KEY and/or EC2_SECRET_KEY are
set, their contents are used as defaults for -acccess_key and
-secret_key.

=cut

sub new {
    my $self = shift;
    my %args = @_;

    my ($id,$secret,$token);
    if (ref $args{-security_token} && $args{-security_token}->can('access_key_id')) {
	$id     = $args{-security_token}->accessKeyId;
	$secret = $args{-security_token}->secretAccessKey;
    }

    $id           ||= $args{-access_key} || $ENV{EC2_ACCESS_KEY}
                      or croak "Please provide -access_key parameter or define environment variable EC2_ACCESS_KEY";
    $secret       ||= $args{-secret_key} || $ENV{EC2_SECRET_KEY}
                      or croak "Please provide -secret_key or define environment variable EC2_SECRET_KEY";

    return bless {
	access_key => $id,
	secret_key => $secret,
       (defined($args{-security_token}) ? (security_token => $args{-security_token}) : ()),
    },ref $self || $self;
}

sub access_key { shift->{access_key } } 
sub secret_key { shift->{secret_key } }

=item $signer->sign($request [,$region] [,$payload_sha256_hex])

Given an HTTP::Request object, add the headers required by AWS and
then sign it with a version 4 signature by adding an "Authorization"
header.

The request must include a URL from which the AWS endpoint and service
can be derived, such as "ec2.us-east-1.amazonaws.com." In some cases