When evaluating a third-party service like Cognito in this case or a mail provider, I either require that it uses an open standard for access like SMTP or the interface that I need to use is small enough that I can wrap it in my own layer of indirection so I can easily mock it and swap it out later. Most of the time I never switch it. But god damn, does it feel good to know that I can move if I need to and I'm not locked in.