public static byte[] decode(byte[] input, int flags) {
    return decode(input, 0, input.length, flags);
  }
Decode the Base64-encoded data in input and return the data in a new byte array.

<p>The padding '=' characters at the end are considered optional, but if any are present, there
must be the correct number of them.

@param input the input array to decode
@param flags controls certain features of the decoded output. Pass {@code DEFAULT} to decode
    standard Base64.
@throws IllegalArgumentException if the input contains incorrect padding
java_src/src/main/java/com/google/crypto/tink/subtle/Base64.java