signHash function
Implementation
Future<String> signHash(Uint8List hash, PairReturnType pair,
[String? encoding]) async {
encoding ??= DEFAULT_OPTS.encode;
final token = jwk(pair.pub, pair.priv);
final signKey = await crypto.EcdsaPrivateKey.importJsonWebKey(
token.toJson(), crypto.EllipticCurve.p256);
final sig = await signKey.signBytes(hash, crypto.Hash.sha256);
return base64Encode(sig);
}