Accessing S3 objects in Salesforce.com - amazon-s3

Question

I am trying to access S3 bucket/object details from Salesforce. I have gone through AWS document and try to generate V4 Signature. It seems like I am missing some parameter and hence getting below error:
The request signature we calculated does not match the signature you provided. Check your key and signing method.
Below is the code snippet:
public class AWSIntegrationS31{
private String accessKeyID = 'SampleAccessKey';
private String secretAccessKey = 'SECRET Key';
private String region = 'ap-south-1';
private String service = 's3';
String host = 's3.ap-south-1.amazonaws.com';
private String httpMethodName;
private String endpoint = 'https://s3.ap-south-1.amazonaws.com'; //test123sfdc1.s3.ap-south-1.amazonaws.com
String content_type = 'application/json'; //'application/x-amz-json-1.0';
private String currentDate;
String expires = '86400'; //24 hrs
String signed_headers;
String S3_signed_headers;
String range = 'bytes=0-9';
String TimeStamp;
String t;
String request_parameters;
String canonical_headers;
String amz_date;
String date_stamp;
public AWSIntegrationS31(){
Datetime now = Datetime.now();
TimeStamp = now.formatGmt('yyyyMMdd')+'T'+now.formatGmt('HHmmss')+'Z';
t = EncodingUtil.urlEncode(TimeStamp, 'UTF-8');
currentDate = now.formatGmt('yyyyMMdd');
amz_date = TimeStamp;
date_stamp = currentDate;
request_parameters = '';
}
public HttpResponse connectAWS(){
// ******************************* 1. Cannoncial Request *******************************
/* Step 1.1 Start with the HTTP request method (GET, PUT, POST, etc.), followed by a newline character. */
httpMethodName = 'GET';
/* Step 1.2 Add the canonical URI parameter, followed by a newline character. */
String canonical_uri = '/';
/* Step 1.3 Add the canonical query string, followed by a newline character. */
String canonical_querystring = request_parameters;
String x_amz_content_sha256= 'e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855';
/* Step 1.4 Add the canonical headers, followed by a newline character. */
canonical_headers = 'host:' + host + '\n' + 'x-amz-content-sha256:' + x_amz_content_sha256 + '\n' + 'x-amz-date:' + amz_date + '\n';
/* Step 1.5 Add the signed headers, followed by a newline character. */
signed_headers = 'host;x-amz-content-sha256;x-amz-date'; //;x-amz-target';
//signed_headers = 'host;x-amz-content-sha256;x-amz-date';
/* Step 1.6 Create payload hash. */
String payload_hash = 'e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855'; //'UNSIGNED-PAYLOAD'; // //EncodingUtil.convertToHex(Crypto.generateDigest('SHA256', Blob.valueOf(''))).toLowerCase();
System.debug('payload_hash....'+payload_hash);
/* Step 1.7: Combine elements to create canonical request. */
String canonical_request = httpMethodName + '\n' + canonical_uri + '\n' + canonical_querystring + '\n' + canonical_headers + '\n' + signed_headers + '\n' + payload_hash;
System.debug('canonical_request...'+canonical_request);
// ******************************* 2. Create string to Sign *******************************
String algorithm = 'AWS4-HMAC-SHA256';
String credential_scope = date_stamp + '/' + region + '/' + service + '/' + 'aws4_request';
String hashRequest = EncodingUtil.convertToHex(Crypto.generateDigest('SHA256', Blob.valueOf(canonical_request))).toLowerCase();
System.debug('hashRequest...'+hashRequest);
String string_to_sign = algorithm + '\n' + amz_date + '\n' + credential_scope + '\n' + hashRequest;
System.debug('Request Parameter....'+request_parameters);
System.debug('StringTosign....'+string_to_sign);
// ******************************* 3. Calculate Signature *******************************
/* Step 3.1. Generate signing key */
Blob signatureKey = Crypto.generateMac('hmacSHA256', Blob.valueOf('aws4_request'),
Crypto.generateMac('hmacSHA256', Blob.valueOf(service),
Crypto.generateMac('hmacSHA256', Blob.valueOf(region),
Crypto.generateMac('hmacSHA256', Blob.valueOf(date_stamp), Blob.valueOf('AWS4'+secretAccessKey))
)
)
);
System.debug('signatureKey..'+signatureKey);
System.debug('signatureKey..2...'+EncodingUtil.base64Encode(signatureKey));
Blob mac = Crypto.generateMac('hmacSHA256', Blob.valueof(string_to_sign),signatureKey);
System.debug('mac...'+mac);
/*Step 3.2. Encode signature (byte[]) to Hex */
String macUrl = EncodingUtil.convertToHex(mac);
System.debug('macURL...1...'+EncodingUtil.convertToHex(mac));
// ******************************* 4. Add Signing Information to the Request *******************************
String authorization_header = algorithm + ' ' + 'Credential=' + accessKeyID + '/' + credential_scope + ',' + 'SignedHeaders=' + signed_headers + ',' + 'Signature=' + macUrl;
System.debug('authorization_header ..'+authorization_header );
// ******************************* 5. Send Request to S3 *******************************
HttpRequest request = new HttpRequest();
request.setMethod('GET');
request.setEndpoint(endpoint);
//request.setBody(request_parameters);
request.setHeader('Content-Type',content_type);
request.setHeader('X-Amz-Date',amz_date);
request.setHeader('x-amz-content-sha256', 'UNSIGNED-PAYLOAD');
request.setHeader('Authorization', authorization_header);
Http http = new Http();
HttpResponse res = http.send(request);
System.debug(res);
System.debug(res.getBody());
return res;
}
}