Base64( HMAC-SHA1( UTF-8-Encoding-Of(YourSecretAccessKey), UTF-8-Encoding-Of( StringToSign ) ) ); in typescript code example

Example: python convert to hmac sha256

import hmac
import hashlib
import base64
dig = hmac.new(b'1234567890', msg=your_bytes_string, digestmod=hashlib.sha256).digest()
base64.b64encode(dig).decode()      # py3k-mode
'Nace+U3Az4OhN7tISqgs1vdLBHBEijWcBeCqL5xN9xg='