This is just my impression but forcing users to sign up for an account would be a problem only if it was directly owned and managed by your product and you were

This is just my impression but forcing users to sign up for an account would be a problem only if it was directly owned and managed by your product and you were the possessor of the account data. Accounts for a third party, particularly for something ubiquitous like Steam, would probably not run afoul of this rule.