Remoting plugin searches for case-sensitive headers

I'm trying to connect a slave to the master using slave.jar, and I keep running into "<url> is not Jenkins". This appears to be because the response does not have the "X-Jenkins-JNLP-Port" header. This is appears to be because nginx is lowercasing the headers, as per the http2 spec. The endpoint resolver should normalize the headers before trying to match against them.