I understand if one borrows a credit card from a fellow it is consider a double loan. I’m assuming being a authorized user on a credit card is considered the same as borrowing in the context of halacha. and what about paying back the loan? wouldn’t their be an issue with paying back the loan directly to the credit card without paying the cardholder and them paying it off?
The person is considered to have borrowed from the cardholder, and therefore should pay back the cardholder.
All the best