/**
	 * signs the request Url for the Amazon API  
	 * @param str      pUrl 			   unsigned Url  
	 * @param str      pSecretAccessKey                it's a hash to sign the Url, 
         *                                                 you get that from the Amazon-Partner network
	 * 						   together with your AccessKey 
	 * @return 		                           signed Url
	 */
	function &signRequestUrl($pUrl,$pSecretAmazonHash){
	    // retrieve Parameter from urls 
	    $arrUrlParts    = parse_url($pUrl);
	    $vParams		= $arrUrlParts['query'];
  	    // parameters are separated by & so we put them in 
            // another array, in there are values like "aa=bb" "xx=yy"	    
            $arrParams		= explode('&',$vParams);
	    // loop and put pair/values in array
	    foreach($arrParams as $vPair){
	    	// easy separating of the name/val by using explode
	    	$arrPair 	   = explode('=',$vPair);
	    	$arrParamsSort[$arrPair[0]] = $arrPair[1];  
	    }
	    // Timestamp needed if there is none present
	    $arrTemp = array_change_key_case($arrParamsSort,CASE_UPPER); 
	    // format from amazon-docs
	    if (empty($arrTemp['TIMESTAMP'])){
	    	$arrParamsSort['Timestamp'] = gmdate('Y-m-d\TH:i:s\Z');
	    }
	    // sort the array, needed to make the Url canonical
	    ksort($arrParamsSort);
	    // canonical means that the parameters are sorted 
            // so it's easier to check if urls are different
	    $vCanonicalString = '';
	    foreach ($arrParamsSort as $vKey => $vVal){
		// rawurlencode => 5.3 should be RFC 3986 compliant 
		// for php versions below this should do the job  
		$vNewVal = str_replace('%7E','~', $vVal);
	    	$vCanonicalString = $vCanonicalString.$vKey.'='.rawurlencode($vNewVal).'&';
	    }
	    // remove last &
	    $vCanonicalString = rtrim($vCanonicalString,'&');
	    // from he amazon docs
	    $vSignString	  = "GET\n".strtolower($arrUrlParts['host']).
            "\n".$arrUrlParts['path']."\n".$vCanonicalString;
	    // generate the hash from the request
	    $vSignature		  = hash_hmac('sha256',$vSignString,$pSecretAmazonHash,true);
	    // and base64 encode it
	    $vSignature 	  = rawurlencode(base64_encode($vSignature));
	    // rebuild the url with the signature
	    $vRet = $arrUrlParts['scheme']."://".$arrUrlParts['host'].
            $arrUrlParts['path']."?".$vCanonicalString."&Signature=".$vSignature;
	    return $vRet;
	}