Simple Example of PHP software changes to comply with Authenticated / Signed Request / Query to Amazon's AWS / Product Advertising API for affiliate websites - which may affect some homeschool websites.

Vision Forum - Homeschooling

Trusted Plans, Advice, and Encouragement from Successful Homeschooling Parents

Amazon documents hint at how to do this, but there's no sample code for PHP programming -
Here's how I got it to work...
// example starts with a typical AWS operation - no keys or timestamp yet
$request = 'Operation=ItemLookup&ResponseGroup=Tags&TagsPerPage=20&Marketplace=us&Version=2008-04-07&ItemId=1604591935';

if ($THE_OLD_UNSIGNED_WAY) {
    // Here's the simple unsigned method that works until August 15 2009
    $request = 'http://webservices.amazon.com/onca/xml?Service=AWSECommerceService&AWSAccessKeyId=YOUR_ACCESS_ID&'.$request;
    $response = file_get_contents($request);
    if ($response) $simple_response = simplexml_load_string($response);
} else {
    // START CHANGES FOR SIGNED REQUEST
    // see http://docs.amazonwebservices.com/AWSECommerceService/latest/DG/index.ht... for more details

    //Substitute your real Access Id here...
    $request = 'Service=AWSECommerceService&'.
        'AWSAccessKeyId=YOUR_ACCESS_ID&'.
        'Timestamp='.gmdate("Y-m-d\TH:i:s\Z").'&'.
        $request;

    // encode url - replace commas w/ %2C, replace colon w/ %3A
    // Could use urlencode($request) here, but $request may already be partially encoded
    $request = str_replace(',','%2C', $request);
    $request = str_replace(':','%3A', $request);

    //break request string into key/value pairs,
    $reqarr = explode('&',$request);

    //sort on byte value
    sort($reqarr);

    // tie back together w/ &'s
    $string_to_sign = implode("&", $reqarr);

    $string_to_sign = "GET\nwebservices.amazon.com\n/onca/xml\n".$string_to_sign;

    //Substitute your real Secret Key here...
    $signature = urlencode(base64_encode(hash_hmac("sha256", $string_to_sign, 'YOUR_SECRET_KEY', True)));

    $request .= '&Signature='.$signature;

    $request = 'http://webservices.amazon.com/onca/xml?'.$request;

    echo 'NEW REQ '.$request;

    // For this example, the above echo should yield:
    // NEW REQ http://webservices.amazon.com/onca/xml?Service=AWSECommerceService&AWSAc...
    // - obviously this is a bogus request as we used placeholders for AccessId and SecretKey

    $response = file_get_contents($request);

    if ($response) $simple_response = simplexml_load_string($response);

    // if your signed request is invalid - AWS will give error response such as:
    // The request signature we calculated does not match the signature you provided. Check your AWS Secret Access Key and signing method. Consult the service documentation for details.

    // more help at: http://mierendo.com/software/aws_signed_query/
}