docs: def SignBuffer(self, in_buffer):
      """Sign a buffer via temp files.
  
      Our signing tool can't sign a buffer, so we work around it using temporary
      files.
  
      Args:
        in_buffer: data to sign
  
      Returns:
        signed data
      """
      precondition.AssertType(in_buffer, bytes)
      with tempfile.NamedTemporaryFile() as temp_in:
        temp_in.write(in_buffer)
        temp_in.seek(0)
        outfile = self.SignFile(temp_in.name)
        with io.open(outfile, "rb") as filedesc:
          return filedesc.read()