Ellen Bagley was delighted when she made her first sale on a popular second-hand clothing app, but just a few minutes later, the thrill turned to shock as the 20-year-old from Linköping in Sweden discovered she’d been robbed. Everything seemed normal when Bagley received a direct message on the platform, which asked her to verify personal details to complete the deal. She clicked the link, which fired up BankID — the ubiquitous digital authorization system used by nearly all Swedish adults....