Setting up Rest Authentication via APex

Can anyone help me implement apex class for authenticating Rest Data Source via Apex?

On creating Authentication Provider is says to implement “ModelDataSourceAuthProvider” class, but SF says it doesn’t exist. Do I need to create the interface myself, if so what methods need to be included? Or, do I need to get the interface via other means?

Thank you,


In addition, is there any impact on SF Governor limits by enabling Apex Proxy or using Apex for authentication?

Thank you