Complete Server Side Auth Flow is missing implementation

[dkbast]

Hi - this library is great :) - I'm currently trying to build a dart web app with server side authentication using session cookies.

For this I need to
a) call verifyIdToken
https://github.com/firebase/firebase-admin-node/blob/8d49b7e67e6867cfe6371d5a76aeadad0743c086/src/auth/base-auth.ts#L212

and
b) cteare a cookie using createSessionCookie
https://github.com/firebase/firebase-admin-node/blob/8d49b7e67e6867cfe6371d5a76aeadad0743c086/src/auth/base-auth.ts#L681

What would be necessary to implement this? Can you point me to the corresponding files/ docs? I'm happy to contribute, but don't really get a grasp of whats going on here.