int getMacLength() throws GeneralSecurityException {
    return Mac.getInstance(macAlgorithm).getMacLength();
  }
Copied from {@link com.google.crypto.tink.subtle.Hkdf#computeHkdf(String, byte[], byte[],
byte[], int)}
java_src/src/main/java/com/google/crypto/tink/hybrid/internal/HkdfHpkeKdf.java