Traefik camel cases response headers

[davidgenn]

Do you want to request a feature or report a bug?

Bug

What did you do?

Traefik in consul-catalogue mode.

What did you expect to see?

Traefik returns backend response headers un-altered.

What did you see instead?

Headers are camel cased eg:

X-MY-APPLICATION-HEADER: 12345

is returned as:

X-My-Application-Header: 12345

Output of traefik version: (What version of Traefik are you using?)

1.3.5

TOML

[consulCatalog]

endpoint = "127.0.0.1:8500"
domain = "service.consul"

frontEndRule = "Host:{{ServiceName}}.{{Domain}},PathPrefixStrip:/{{ServiceName}}"
prefix = "traefik"

[ldez]

RFC 7230 (and also 7540) states:

"Each header field consists of a case-insensitive field name followed by a colon (":"), optional leading whitespace, the field value, and optional trailing whitespace."

Golang http server rewrites all headers in a canonical way and your backends shouldn't rely on case sensitivity golang/go#5022.

Duplicate of #1756 #466