code: @NotNull
      public static byte[] decodeWebSafe(byte[] source, int off, int len)
              throws Base64DecoderException {
          return decode(source, off, len, WEBSAFE_DECODABET);
      }
docs: Decodes web safe Base64 content in byte array format and returns
  the decoded byte array.
  Web safe encoding uses '-' instead of '+', '_' instead of '/'
  
  @param source the Base64 encoded data
  @param off    the offset of where to begin decoding
  @param len    the length of characters to decode
  @return decoded data