public static String encodeToString(byte[] input, int flags) {
    try {
      return new String(encode(input, flags), "US-ASCII");
    } catch (UnsupportedEncodingException e) {
      // US-ASCII is guaranteed to be available.
      throw new AssertionError(e);
    }
  }
Base64-encode the given data and return a newly allocated String with the result.

@param input the data to encode
@param flags controls certain features of the encoded output. Passing {@code DEFAULT} results
    in output that adheres to RFC 2045.
java_src/src/main/java/com/google/crypto/tink/subtle/Base64.java