If an authorized user account is reported in the authorized user's credit report, the account will be included in the score calculation just as it would if they were the primary account holder as long as the account is a legitimate authorized user account (see FICO 08 authorized user update).
If the account is in good standing without any negative information (has an excellent payment history and a low balance in proportion to the credit limit), then the authorized user's credit scores will benefit from the account being added to their credit reports. However, if the account has any negative information (negative payment history or high balance in comparison to the available credit limit), then the added account will have a negative impact on the authorized user's credit scores.