You can download the .CS source file here.
This file should be placed in the dashCommerce
...\App_Code\Services\PaymentProvider\...
directory and the following section added to your web.config with the appropriate values:
<PaymentService acceptCreditCards="true" defaultProvider="CyberSourcePaymentProvider">
<providers>
<clear/>
<add
merchantID="your merchant ID"
keysDirectory="your keys directory"
sendToProduction="false"
connectionLimit="-1"
authService="true"
captureService="true"
currencyCode="USD"
name="CyberSourcePaymentProvider"
type="Commerce.Providers.CyberSourcePaymentProvider"/>
</providers>
</PaymentService>
Note that you'll need to comment out or remove other Payment Provider entries in web.config.