def read_json_base64
      str = read_json_string
      m = str.length % 4
      if m != 0
        # Add missing padding
        (4 - m).times do
          str += '='
        end
      end
      Base64.strict_decode64(str)
    end
def read_json_base64
      str = read_json_string
      m = str.length % 4
      if m != 0
        # Add missing padding
        (4 - m).times do
          str += '='
        end
      end
      Base64.strict_decode64(str)
    end
Reads a block of base64 characters, decoding it, and returns via str