Presigned URL for S3 Object Get

[berlin2]

Do you have an example for generating a presigned URL for a S3 Object Get with a temporary session id?

[berlin2]

This is what I came up with:

const aws_sha_256 = 'AWS4-HMAC-SHA256';
mysign() {
  String bucket = 'name_of_bucket.s3.amazonaws.com';
  String image = Uri.encodeComponent('xyz.jpg');
  String date = SigV4.generateDatetime();
  String date1 = date.substring(0, 8);
  String region = 'us-east-2';
  int expires = 86400; // in seconds. 86400 = 24hours, 604800 = 7days

  String credential = '$aws_access_key_id/$date1/$region/s3/aws4_request';

  //https://docs.aws.amazon.com/AmazonS3/latest/API/sigv4-query-string-auth.html
  final params = {
    'X-Amz-Algorithm': aws_sha_256,
    'X-Amz-Credential': credential,
    'X-Amz-Date': date,
    'X-Amz-Expires': expires.toString(),
    'X-Amz-SignedHeaders': 'host',
    'X-Amz-Security-Token': aws_session_token
  };
  

  final canonicalRequest = '''GET
/$image
${SigV4.buildCanonicalQueryString(params)}
host:$bucket

host
UNSIGNED-PAYLOAD''';
  
  final hashedCanonicalRequest = SigV4.hashCanonicalRequest(canonicalRequest);
  final credentialScope = SigV4.buildCredentialScope(date, region, 's3');
  final stringToSign = SigV4.buildStringToSign(date, credentialScope, hashedCanonicalRequest);
  final signingKey = SigV4.calculateSigningKey(aws_secret_access_key, date1, region, 's3');
  final signature = SigV4.calculateSignature(signingKey, stringToSign);

  String url = 'https://$bucket/$image?';
  url = url + 'X-Amz-Algorithm=$aws_sha_256&';
  url = url + 'X-Amz-Credential=${Uri.encodeComponent(credential)}&';
  url = url + 'X-Amz-Date=$date&';
  url = url + 'X-Amz-Expires=$expires&';
  url = url + 'X-Amz-SignedHeaders=host&';
  url = url + 'X-Amz-Security-Token=${Uri.encodeComponent(aws_session_token)}&';
  url = url + 'X-Amz-Signature=$signature';
  print(url);

}

[samuelchanx]

@berlin2 works like a charm, thanks!