I understand state can be certified and this is up to the canister developer to determine what state needs to be certified. But when one queries for this state is the verification of the certified state done by IC or is there a way to get the certified state along with the proof and have the canister developer valid the certification. I guess I am confused about the usage of this capability. Thanks in advance
For HTTP requests (see spec here) the certificate check is done by the boundary nodes. If you want to verify manually, you can turn the HTTP request into an API call (e.g. with dfx canister call <canister> http_request) and follow the spec for verification
In general the certificate needs to be sent along with the response so that the caller can check the validity. You can read more about it here: https://internetcomputer.org/docs/current/tutorials/developer-journey/level-3/3.3-certified-data/