I think it's:
there is currently no support for client-cert X.509 auth yet on Espruino
i.e., the client (Espruino) needs to authenticate to AWS using a client certificate and it sounds like what you have doesn't support that.
@tve started
Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
I think it's:
i.e., the client (Espruino) needs to authenticate to AWS using a client certificate and it sounds like what you have doesn't support that.