In META-INF/services/io.undertow.websockets.jsr.WebsocketSslProvider, io.undertow.websockets.jsr.DefaultWebSocketSslProvider is defined but they don't exist. The "Client" is missing.

It should be META-INF/services/io.undertow.websockets.jsr.WebsocketClientSslProvider and io.undertow.websockets.jsr.DefaultWebSocketClientSslProvider.

Thanks again Masuda-san! https://twitter.com/masudanaika/status/461873601784713216