ForwardedHeaderSupport

The ForwardedHeaderSupport plugin (previously known as feature) allows you to handle reverse proxy headers to get information about the original request when it's behind a proxy.

ForwardedHeaderSupport handles the standard Forwarded header (RFC 7239)
XForwardedHeaderSupport handles the non-standard (but standard de-facto) X-Forwarded-Host/X-Forwarded-Server, X-Forwarded-For, X-Forwarded-By, X-Forwarded-Proto/X-Forwarded-Protocol and X-Forwarded-SSL/Front-End-Https

Usage

These plugins don't require any special configuration. You can install any of the two depending on your reverse proxy, but since the standard is the Forwarded header, you should favor it whenever possible.

install(ForwardedHeaderSupport)

install(XForwardedHeaderSupport)

Request information

You can see all the available request properties on the Requests page.

The proxy request information

You can read the raw or local request information, read from the received normal headers and socket properties, that correspond to the proxy request using the request.local property:

val scheme = request.local.scheme
val version = request.local.version
val port = request.local.port
val host = request.local.host
val uri = request.local.uri
val method = request.local.method
val remoteHost = request.local.remoteHost

The original request information

You can read the original request information, read from the Forwarded or X-Forwarded-* headers with fallback to the raw headers, that corresponds to original client request using the request.origin property:

val scheme = request.origin.scheme // Determined from X-Forwarded-Proto / X-Forwarded-Protocol / X-Forwarded-SSL
val version = request.origin.version
val port = request.origin.port // Determined from X-Forwarded-Host / X-Forwarded-Server
val host = request.origin.host // Determined from X-Forwarded-Host / X-Forwarded-Server
val uri = request.origin.uri
val method = request.origin.method
val remoteHost = request.origin.remoteHost // Determined from X-Forwarded-For

In the cases where you need the X-Forwarded-By (the interface used for the socket), you can access the raw X-Forwarded properties with:

val forwardedValues: List<ForwardedHeaderSupport.ForwardedHeaderValue> = call.attributes[ForwardedHeaderSupport.ForwardedParsedKey]

data class ForwardedHeaderValue(val host: String?, val by: String?, val forParam: String?, val proto: String?, val others: Map<String, String>)

Header description

The standard Forwarded header looks like this:

Forwarded: by=<identifier>; for=<identifier>; host=<host>; proto=<http|https>

by - The interface where the request came in to the proxy server.
for - The client that initiated the request and subsequent proxies in a chain of proxies.
host - The Host request header field as received by the proxy.
proto - Indicates which protocol was used to make the request (typically "http" or "https").

Last modified: 27 May 2021