sign method
Create a signature of the body
with key
return the signature as bytes
Implementation
@override
Uint8List sign(JWTKey key, Uint8List body) {
assert(key is SecretKey, 'key must be a SecretKey');
final secretKey = key as SecretKey;
final hmac = Hmac(_getHash(name), utf8.encode(secretKey.key));
return Uint8List.fromList(hmac.convert(body).bytes);
}