SockJsClient doesn't propagate "subProtocols" and "extensions" to the handshake request [SPR-12030] #16646
Description
Artem Bilan opened SPR-12030 and commented
Since "Sec-WebSocket-Protocol" and "Sec-WebSocket-Extensions" headers are filtered from handshakeHeaders in the AbstractWebSocketClient.doHandshake, the concrete AbstractWebSocketClient should take care about about those headers according to the target implementation.
As a solution SockJsClient has to "repopulate" those headers to the handshakeHeaders for further handshake fallback chain.
Referenced from: commits 41cdc92