Is it possible to find a user by searching with a Username in AWS Lambda? The GetUserCommand does not seem to accept a Username as a parameter. The input shape does not include a Username parameter. Am I misunderstanding?
The command you are referring to only needs an access token. Since the access token belongs to your user it will return information about her/him. You don't really need to provide a username. Would be kind of redundant.
If you want to get information about a user as an admin (so not as a user that is currently signed in), then you need another method: AdminGetUserCommand. There you can specify which username you want using AdminGetUserCommandInput.