Reversy proxy - how to modify header request

1. The problem I’m having:

I am trying to reverse proxy to an external server (Internet) from LAN.
On that reversy_proxy I need to change the host and referrer headers, but with everything I do I can’t modify these headers.

2. Error messages and/or full log output:

2024/05/02 11:25:20.240 ←[34mINFO←[0m   http.log.access handled request {"request": {"remote_ip": "::1", "remote_port": "59955", "client_ip": "::1", "proto": "HTTP/1.1", "method": "GET", "host": "localhost:8080", "uri": "/xxx/yyyyy/GETPHRASES/Page", "headers": {"Sec-Fetch-Site": ["same-origin"], "Sec-Fetch-Dest": ["empty"], "Referer": ["http://localhost:8080/xxx/yyyyy/runclient/Page"], "Accept-Language": ["es-AR,es-US;q=0.9,es-419;q=0.8,es;q=0.7"], "X-Vtscadaphraseids": ["REASON_STR_HOSTNOTINLIST"], "Sec-Ch-Ua-Platform": ["\"Windows\""], "Sec-Fetch-Mode": ["cors"], "User-Agent": ["Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/ Safari/537.36"], "Accept-Encoding": ["gzip, deflate, br, zstd"], "Connection": ["keep-alive"], "Sec-Ch-Ua": ["\"Chromium\";v=\"124\", \"Google Chrome\";v=\"124\", \"Not-A.Brand\";v=\"99\""], "X-Vtscadaanywhere": ["true"], "Sec-Ch-Ua-Mobile": ["?0"], "Accept": ["*/*"]}}, "bytes_read": 0, "user_id": "", "duration": 0.0647577, "size": 66, "status": 200, "resp_headers": {"Server": ["Caddy", "VTScada"], "Cache-Control": ["no-cache, no-store"], "Date": ["Thu, 2 May 2024 11:25:20 GMT"], "Content-Type": ["application/json; charset=\"utf-8\""], "Content-Length": ["66"]}}

3. Caddy version:


4. How I installed and ran Caddy:

I created a caddyfile in same folder as caddy.exe
inside a bat file
caddy run

a. System environment:

Windows 10 Pro 22H2

b. Command:

caddy run

c. Service/unit/compose file:

d. My complete Caddy config:

:8080 {
	reverse_proxy /xxx* {
		header_up host {upstream_hostport}
	rewrite / /xxx/

5. Links to relevant resources:

The “full log output” you posted on point 2 is the access-log and the "host": "localhost:8080" from "request" is how the request arrived at Caddy.

If you want to see the more details from the reverse proxy communication with, you can enable debug logging and watch out for http.handlers.reverse_proxy.

To modify the “Referer”, which has the original value of http://localhost:8080/xxx/yyyyy/runclient/Page you can use again header_up (see reverse_proxy (Caddyfile directive) — Caddy Documentation):

header_up sets, adds (with the + prefix), deletes (with the - prefix), or performs a replacement (by using two arguments, a search and replacement) in a request header going upstream to the backend.

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Thank you.

Now is possible to see the changes for host header.

To change Referer header string, only with regex or is there a function like replace?



There is, see above excerpt from the reverse_proxy documentation:

or performs a replacement (by using two arguments, a search and replacement)

For example, this should be working:

header_up Referer "runclient" "chicken-dinner"

Ok, thanks.

In documentation is not explained how to use regex sintax with variables.

I need to change host in Referer header to upstream variable

This code doesn’t work

Header_up Referer ‘{upstream}{Referer}(/tmb/.)’

I tried to concatenate upstream variable with Referer header without host and port.


Does your Referer always contain localhost:8080?
If so, use this:

header_up Referer "localhost:8080" "{upstream_hostport}"


header_up Referer "http://localhost:8080" "https://{upstream_hostport}"

Take care about case sensitivity regarding caddy directives. Header_up is wrong, it must be header_up.

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