Every time I referee a paper, I dream of a system which would allow me to ask the author a question without troubling the editors. It would save time for everyone involved, most importanly the referee; in my case it would probably half the refereeing time.
Here is the system I envision: together with the paper, the journal would give the referee a link to a secure web form where the referee could type a question which would automatically be emailed to the corresponding author, who in turn could reply in a similar web form. Of course, the editors should have access to the logs of these exchanges, and the system should be set up so that the exchanges (if any) can only be initiated by the referee.
Question. Has this ever been implemented? Are there reasons this cannot (or should not) be implemented in mathematics journals?