Hey @Gekctek
We have an update for you and the good news is, we will get there, but it will take some time:
Currently, the HTTP gateways directly reply to any OPTIONS request with the default headers. We have now updated the behavior such that OPTIONS requests are passed on to the canister. If the canister provides a valid response, the HTTP gateway returns it to the client. Otherwise, the HTTP gateway injects its default response and remembers for 1 day that the canister is not providing proper responses (this is to reduce the latency and load).
However, we have not yet activated this behavior as none of the canisters that we tested with actually support OPTIONS requests. The asset canister treats every requests as a GET (independent of the actual request method). NNS and II dapp are the same. The only dapp that somewhat handles OPTIONS is juno.build, which returns a 405 Method not supported error. We have brought it up internally and hopefully, we can get support for that soon (at least in the asset canister).
What kind of canister do you intend to use? Do you have your own canister or do you rely on the asset canister?
UPDATE: Just in case you are interested: this is the corresponding PR on the HTTP gateway