I received this response in an email from an author, is it common to ask for this data?
-Before can you please send us your themeforest Purchased license key files along with your Store URL with login details. Also send us some screenshots about your issues.
Thank You
The purchase code - yes, but usually you would need to register using a purchase code to access support.
The website url and access - depending on what the issue is then it may well be necessary for the author to be able to help.
They definitely won’t be able to do anything if they cannot see/investigate the issue
I have already accessed the website, now they are asking for username and password for the themeforest account
For themeforest no / there’s no obvious reason for that.
Assuming that you’ve provided the purchase code then they can verify the purchase etc.
Have you asked them why they need that? That would give them access to all of your purchases and downloads which is a fairly clear cut train not to be able to provide it