I'm trying to create the final step of this example in Flutter and I can't get it right for some reason:
<https://docs.aws.amazon.com/general/latest/gr/sigv4-calculate-signature.html>

Using their Signing Key + String to sign they get this resulting signature:
`5d672d79c15b13162d9279b0855cfba6789a8edb4c82c400e06b5924a6f2b5d7`

Using the exact same key / string to sign I end up with:
`fe52b221b5173b501c9863cec59554224072ca34c1c827ec5fb8a257f97637b1`

Here is my code:

```
var testSigninKey =
'c4afb1cc5771d871763a393e44b703571b55cc28424d1a5e86da6ed3c154a4b9';
var testStringToSign = 'AWS4-HMAC-SHA256' + '\n' +
      '20150830T123600Z'  + '\n' +
      '20150830/us-east-1/iam/aws4_request'  + '\n' +
      'f536975d06c0309214f805bb90ccff089219ecd68b2577efef23edd43b7e1a59';    

var hmac1 = Hmac(sha256, utf8.encode(testSigninKey));
var digest1 = hmac1.convert(utf8.encode(testStringToSign));
print(digest1);
print(hex.encode(digestBytes.bytes));
//both print: fe52b221b5173b501c9863cec59554224072ca34c1c827ec5fb8a257f97637b1

```