How to verify a DER ECDSA signature with bitcore-lib

Dear forumers,
I’m a long-time lurker but this time I’m afraid to need your help here.

I need to pickup any raw transaction out there and test if the scriptsig inside is valid using my browser based javascript. I’m not generating the signatures with bitcore-lib, they are coming from another source (offline wallet).

I’ve tried with the crypto.ECDSA.verify without success (my sig argument is a simple object with r and s arrays), and I haven’t figured out where the old Transaction.applySignature has come (and if the method should be the same).

Any hints?
Thank you!