AWS Signature for REST Get & Post

I was able to implement this using a Script Snap. Code for the Script Snap is below in case this can help someone else. Please note this is only for a GET request, and also note the HTTP Headers in the REST Get Snap.

/*
Purpose of this script is to derive a signing key and signature for AWS Signature Version 4 to enable calling an AWS based API GET method
https://docs.aws.amazon.com/general/latest/gr/signature-v4-examples.html
https://docs.aws.amazon.com/general/latest/gr/sigv4-signed-request-examples.html
*/

try { load("nashorn:mozilla_compat.js"); } catch(e) { }

importPackage(com.snaplogic.scripting.language);
importPackage(java.util);

importClass(javax.crypto.Mac);
importClass(javax.crypto.spec.SecretKeySpec);
importClass(org.apache.commons.codec.binary.Base64);
importClass(org.apache.commons.codec.digest.DigestUtils);
importClass(javax.xml.bind.DatatypeConverter);

var impl = {
    input : input
    , output : output
    , error : error
    , log : log

    ,execute : function () 
    {
        //----------------------------------------------------------
        // Enter your variables here
        //----------------------------------------------------------
        var secretKey = ''; // Your Secret Key
        var accessKey = ''; // Your Access Key
        var regionName = ''; //e.g.: us-east-1
        var serviceName = ''; //e.g.: execute-api
        var endpoint = ''; //e.g.: https://subdomain.domain.com/resource/id
        var host = ''; //e.g.: subdomain.domain.com
        var canonical_uri = ''; //e.g.: /resource/id
        var canonical_querystring = ''; //e.g.: Param1=value&Param2=value
        //----------------------------------------------------------
        
        var method = 'GET';
        var dateStamp = impl.getDateStamp();
        var amzdate = impl.getDateTimeStamp();
        var canonical_headers = 'host:' + host + '\n' + 'x-amz-date:' + amzdate + '\n';
        var signed_headers = 'host;x-amz-date';
        var payload_hash =  DigestUtils.sha256Hex('');
        var canonical_request = method + '\n' + canonical_uri + '\n' + canonical_querystring + '\n' + canonical_headers + '\n' + signed_headers + '\n' + payload_hash;
        var algorithm = 'AWS4-HMAC-SHA256';
        var credential_scope = dateStamp + '/' + regionName + '/' + serviceName + '/' + 'aws4_request';
        var string_to_sign = algorithm + '\n' +  amzdate + '\n' +  credential_scope + '\n' +  DigestUtils.sha256Hex(canonical_request); 
        var signing_key = impl.getSignature(secretKey, dateStamp, regionName, serviceName);
        var signature = impl.base64toHEX(impl.HmacSHA256( string_to_sign, signing_key ));
        var authorization_header = algorithm + ' ' + 'Credential=' + accessKey + '/' + credential_scope + ', ' +  'SignedHeaders=' + signed_headers + ', ' + 'Signature=' + signature;
        
        var wrapper = new java.util.HashMap();
        wrapper.put("authorization", authorization_header );
        wrapper.put("url", endpoint );
        wrapper.put("host", host );
        wrapper.put("amzdate", amzdate );
        
        this.output.write(wrapper);
    }
    
    , getSignature : function ( secretKey, dateStamp, regionName, serviceName ) 
    {
        regionName = regionName || '';
        serviceName = serviceName || '';
        dateStamp = dateStamp || '';
        
        var kSecret = (new java.lang.String( "AWS4" + secretKey )).getBytes("UTF8");
        var kDate = impl.HmacSHA256(dateStamp, kSecret);
        var kRegion = impl.HmacSHA256(regionName, kDate);
        var kService = impl.HmacSHA256(serviceName, kRegion);
        var kSigning = impl.HmacSHA256("aws4_request", kService);
        return kSigning;
    }
    
    , HmacSHA256 : function ( data, secretKey ) 
    {
        var algorithm = "HmacSHA256";
        var mac = Mac.getInstance( algorithm );
        mac.init(new SecretKeySpec( secretKey, algorithm ) );
        return mac.doFinal( data.getBytes("UTF8") );
    }
    
    , getDateStamp : function ()
    {
        // Must be YYYYMMDD format
        var d = new Date();
        var dateStamp = d.getFullYear();
        dateStamp += ('0' + (d.getMonth()+1)).slice(-2);
        dateStamp += ('0' + d.getDate()).slice(-2);
        return dateStamp;
    }

    , getDateTimeStamp : function ()
    {
        // Must be YYYYMMDDTHHMMSSZ format
        var d = new Date();
        var dateTimeStamp = impl.getDateStamp();
        dateTimeStamp += 'T';
        dateTimeStamp += ('0' + d.getHours()).slice(-2);
        dateTimeStamp += ('0' + d.getMinutes()).slice(-2);
        dateTimeStamp += ('0' + d.getSeconds()).slice(-2);
        dateTimeStamp += 'Z';
        return dateTimeStamp;
    }
    
    , base64toHEX : function( guid ) 
    {
        return DatatypeConverter.printHexBinary( guid ).toLowerCase();
    }
    
};

var hook = new com.snaplogic.scripting.language.ScriptHook(impl);