I've an IoT server written in Go that IoT devices connect to with TLS. It works fine with a variety of devices. Now I'm trying to connect to it with a new device using a Calypso Wifi module but it wont connect and fails with tls: no cipher suite supported by both client and server.
Debugging by littering the Go TLS code with prints it turns out that it fails because the call to supportsECDHE returns false. It's using secp256r1 ecdsa keys and both server and device are set to use TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256.
Debugging further it looks like the Calypso module is not setting any supportedPoints in its client hello (hs.clientHello.supportedPoints) so then supportsECDHE will always return false.