HTTP Connection header is not mandatory but web socket code expects it.

[GrahamDumpleton]

Describe the bug

The HTTP Connection header is not mandatory and should be defaulted to keep-alive in HTTP/1.1.

Even so, the web socket code expects it to exist and will error if not supplied the header.

        start = strstr(handshake, "\r\nConnection: ");
        if (!start) { err("missing Connection header"); return 0; }

Source:

KasmVNC/common/network/websocket.c

Lines 684 to 685 in 5ea11df

	start = strstr(handshake, "\r\nConnection: ");
	if (!start) { err("missing Connection header"); return 0; }

KasmVNC Details

Using kasmweb/alpine-320-desktop:1.16.1 from Docker Hub.