SSRS from Cloud

SSAS and SSRS
1

Out SSRS reports were setup using Windows Authentication and they used built-in UserID as parameter and get the user email from that to fetch data from the DB.

However, in cloud - we can't use Windows Authentication anymore.
So, now we need to pass the user email in the URL as parameter.
My question is:

Can we still use the built-in UserID parameter - because in mixed mode, it will have to use the credentials of the user.

2
  1. have you moved to the cloud yet?
  2. How will your current users access the cloud reporting? Will they log in using their current user account and password?
  3. why are you using a lookup table to fetch the user email if you already have their UserID?