How to identify authentification error type in AWS Amplify using Kotlin?

I want to display different errors to the user when they are logging in through AWS Amplify using Kotlin. This is what I have set up as my last parameter of Amplify.Auth.signIn():

{ error ->
     inputEmail.error = "Check if the e-mail is valid"
     inputPassword.error = "Check if the password is valid"
})

“error” is a “Throwable?” which I wanted to cast to various AWS exceptions and check whether the cast was a success. Yet all of the AWS Amplify exceptions are based on the Java version of “Throwable”. Is there a way to make these casts work or is there an alternative way to identify error types in Kotlin?

Answer

The last argument in the signIn(...) method is of type Consumer<AuthException>. This is a function that accepts an AuthException, and does something with it. So, you shouldn’t need to downcast the input.

There are a few types exception that extend AuthException.

As in this answer, I suggest is to exhaust those types using a when construct. Paraphrasing:

when (error) {
    is SessionUnavailableOfflineException -> doSomething()
    is InvalidAccountTypeException -> doSomethingElse()
    // etc.
}

You can also check for errors in the active auth session with fetchAuthSession(...):

Amplify.Auth.fetchAuthSession(
    { result ->
        val cognitoAuthSession = result as AWSCognitoAuthSession
        if (AuthSessionResult.Type.FAILURE == cognitoAuthSession.identityId.type) {
            // do stuff
        }
    },
    { error -> Log.e("AuthQuickStart", error.toString()) }
)