whole_class.kt

private val oneTapClient: SignInClient by lazy {
    Identity.getSignInClient(this)
}

private val loginResult =
    registerForActivityResult(ActivityResultContracts.StartIntentSenderForResult()) {
        val credential = oneTapClient.getSignInCredentialFromIntent(it.data)
        val idToken = credential.googleIdToken
        val username = credential.id
        val password = credential.password
        when {
            idToken != null -> {
                // Got an ID token from Google. Use it to authenticate
                // with your backend.
                Log.d(TAG, "Got ID token.")
            }
            password != null -> {
                // Got a saved username and password. Use them to authenticate
                // with your backend.
                Log.d(TAG, "Got password.")
            }
            else -> {
                // Shouldn't happen.
                Log.d(TAG, "No ID token or password!")
            }
        }
    }

private val signUpResult =
    registerForActivityResult(ActivityResultContracts.StartIntentSenderForResult()) {
        try {
            val credential = oneTapClient.getSignInCredentialFromIntent(it.data)
            val idToken = credential.googleIdToken
            when {
                idToken != null -> {
                    // Got an ID token from Google. Use it to authenticate
                    // with your backend.
                    Log.d(TAG, "Got ID token.")
                }
                else -> {
                    // Shouldn't happen.
                    Log.d(TAG, "No ID token!")
                }
            }
        } catch (e: Exception) {
            Log.e(TAG, e.message, e)
            Log.v(TAG, "Hash is: ${getCertificateSHA1Fingerprint()}")
        }
    }

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_one_tap_authentication)

    signin()
}

private fun signin() {
    lifecycleScope.launch(errorHandler { signup() }) {
        val result = oneTapClient.suspendBeginSignInRequest(buildSignInRequest())
        loginResult.launch(
            IntentSenderRequest.Builder(result.pendingIntent)
                .build()
        )
    }
}

private fun buildSignInRequest() = BeginSignInRequest.builder()
    .setPasswordRequestOptions(
        BeginSignInRequest.PasswordRequestOptions.builder()
            .setSupported(true)
            .build()
    )
    .setGoogleIdTokenRequestOptions(
        BeginSignInRequest.GoogleIdTokenRequestOptions.builder()
            .setSupported(true)
            // Your server's client ID, not your Android client ID.
            .setServerClientId(getString(R.string.one_tap_client_id))
            // Only show accounts previously used to sign in.
            .setFilterByAuthorizedAccounts(true)
            .build()
    )
    .build()

private fun signup() {
    lifecycleScope.launch(errorHandler()) {
        val result = oneTapClient.suspendBeginSignInRequest(buildSignupRequest())
        signUpResult.launch(
            IntentSenderRequest.Builder(result.pendingIntent)
                .build()
        )
    }
}

private fun errorHandler(onError: (() -> Unit)? = null): CoroutineExceptionHandler {
    return CoroutineExceptionHandler { _, e ->
        onError?.invoke()
        Log.e(
            TAG,
            e.localizedMessage ?: "",
            e
        )
    }
}


private fun buildSignupRequest() = BeginSignInRequest.builder()
    .setGoogleIdTokenRequestOptions(
        BeginSignInRequest.GoogleIdTokenRequestOptions.builder()
            .setSupported(true)
            .setServerClientId(getString(R.string.one_tap_client_id))
            .setFilterByAuthorizedAccounts(false)
            .build()
    )
    .build()


companion object {
    const val TAG = "OneTapAuthentication"
}