golang with fastcgi how to read REMOTE_USER

Short: How can I read the CGI var REMOTE_USER on golang using fastcgi?

Long:
I'm trying to write a program in go to work behind a httpd using fcgi over a socket. The httpd does the ssl termination and provides basic auth. I need to read $REMOTE_USER, but I cannot in golang, while I can in perl.

My code is based on this fcgi example. I try

func homeView(w http.ResponseWriter, r *http.Request) {	   	
	user, pass, authok := r.BasicAuth()

But authok is always false, user and pass remain empty, although I know for sure that the authorization (done by httpd) was OK. To eliminate other errors, I have done it in perl:

my $socket = FCGI::OpenSocket("/run/fcgi-check.sock", 5);
my $q = FCGI::Request(\*STDIN, \*STDOUT, \*STDERR, \%ENV, $socket);

while ($q->Accept() >= 0) {
    my $c = CGI::Simple->new;
    my $user_id      = $c->remote_user(); 

and it works fine in perl.

To debug, I printed the output of r.Header and I got:

map[Authorization:[]

Am I right that the header that go sees does no hold any information about any authorization? But it does in perl.

Here is a full but minimal golang code example that demonstrates the problem (on OpenBSD 5.8 with go version go1.4.2 openbsd/amd64 and OpenBSDs httpd with 'authenticate "/" with restricted_users' in httpd.conf.

package main

import (
        "github.com/gorilla/mux"
        "io"
        "log"
        "fmt"
        "net"
        "net/http"
        "net/http/fcgi"
)


func homeView(w http.ResponseWriter, r *http.Request) {
        headers := w.Header()
        headers.Add("Content-Type", "text/html")
        headers.Add("Cache-Control", "no-cache, no-store, must-revalidate")
        headers.Add("Pragma", "no-cache")
        headers.Add("Expires", "0")
        r.ParseForm()

        user, pass, authok := r.BasicAuth()

        if authok {
                io.WriteString(w, fmt.Sprintln("Auth OK"))
                io.WriteString(w, fmt.Sprintln("user is: "+user+", pass is: "+pass))
        } else {
                io.WriteString(w, fmt.Sprintln("Auth NOT OK"))
        }
}

func main() {

        r := mux.NewRouter()
        r.HandleFunc("/check/", homeView)

    var err error
        listener, err := net.Listen("unix", "/run/fcgi-check.sock")
        if err != nil {
                log.Fatal(err)
        }
        defer listener.Close()

        err = fcgi.Serve(listener, r)
        if err != nil { log.Fatal(err)}
}

Help will be appreciated!

Thanks in advance!
T.

Go 1.9 will expose cgi environment variables. As seen in this closed ticket:

https://go-review.googlesource.com/c/40012

While @JimB is correct on that you're wrong in your approach, I'll answer the question as stated.

The net/http/fcgi package uses the machinery of net/http/cgi to populate an instance of http.Request—which is passed to your handler—with "parameters" (key/value pairs) submitted by the webserver during the FastCGI session (call).
This is done here.

Now if you'll inspect the relevant bit of the net/http/cgi code, you'll see that the variables which are not mapped to specific dedicated fields of http.Request get converted to HTTP "headers".

This means, <s>your code should be able to access the variable you need using something like</s>

ruser := r.Header.Get("Remote-User")

Update 2015-12-02: the reseach performed by @JimB and the OP showed that there's apparently no way to read the REMOTE_USER variable under FastCGI. Sorry for the noise.

The simple answer (as of go version 1.4.2) is that go currently does not support the transfer of CGI variable REMOTE_USER.

This core change to the fcgi package is in review and is close to being merged. If it's no longer relevant to you, hopefully it will be useful to others.