AsymmetricKeyEncryptor is missing from the v3 SDK

The AsymmetricKeyEncryptor class appears to be missing from the SDK.  Updating datasource credentials relies on the usage of this class to encrypt the new credentials as shown in this link: 

https://docs.microsoft.com/en-us/power-bi/developer/automation/configure-credentials?tabs=sdk3

Can someone please help with this issue?

Thanks.