问如何将一下这两个方法的java代码转换为c#代码？

public static byte[] hmac256(byte[] key, String msg) throws Exception {

Mac mac = Mac.getInstance("HmacSHA256");

SecretKeySpec secretKeySpec = new SecretKeySpec(key, mac.getAlgorithm());

mac.init(secretKeySpec);

return mac.doFinal(msg.getBytes(UTF8));

}

public static String sha256Hex(String s) throws Exception {

MessageDigest md = MessageDigest.getInstance("SHA-256");

byte[] d = md.digest(s.getBytes(UTF8));

return DatatypeConverter.printHexBinary(d).toLowerCase();

}