Basic Authentication for static resources - http

Question

How can I add basic authentication to my static resources? With the code below, I'm able to view any files that are in the labels folder. I know in this question it was explained how to do it. But how would would I set the header when a http.ResponseWriter is not used?
package main
import (
"github.com/gorilla/mux"
"log"
"net/http"
"os"
)
func main() {
port := GetPort()
log.Println("[-] Listening on...", port)
r := mux.NewRouter()
r.PathPrefix("/labels/").Handler(http.StripPrefix("/labels/", http.FileServer(http.Dir("./labels/"))))
err := http.ListenAndServe(port, r)
log.Fatal(err)
}
// GetPort is for herkou deployment
func GetPort() string {
port := os.Getenv("PORT")
if port == "" {
port = "4747"
log.Println("[-] No PORT environment variable detected. Setting to ", port)
}
return ":" + port
}

Answer 1

Create a wrapper around each handler to pass the request from the authentication middleware which will forward the request further after authentication is done else return the response with error as
func authentication(next http.Handler) http.Handler {
return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
log.Println("Executing authentication")
next.ServeHTTP(w, r)
})
}
// open the dialog to download pdf files.
func dowloadPdf(w http.ResponseWriter, r *http.Request) {
w.Header().Set("Content-Disposition", "attachment; filename=YOUR_FILE")
w.Header().Set("Content-Type", r.Header.Get("Content-Type"))
w.Write([]byte("File downloaded"))
}
func main(){
pdfHandler := http.HandlerFunc(dowloadPdf)
http.Handle("/servepdf", authentication(pdfHandler))
http.ListenAndServe(":3000", nil)
}
But if I consider the fact there is no need to have authentication when serving static files like html, css, js etc. It would be better to create a handler to serve pdf files after authenticating users.
You can also use negorni middlewares with gorilla mux rather than creating custom middlewares.

Answer 2

package main
import (
"github.com/gorilla/mux"
"log"
"net/http"
"os"
)
func main() {
port := GetPort()
log.Println("[-] Listening on...", port)
r := mux.NewRouter()
r.PathPrefix("/labels/").Handler(http.StripPrefix("/labels/", ServeLabels(http.FileServer(http.Dir("./labels/")))))
err := http.ListenAndServe(port, r)
log.Fatal(err)
}
func ServeLabels(h http.Handler) http.Handler {
return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
w.Header().Set("WWW-Authenticate", `Basic realm="mydomain"`)
h.ServeHTTP(w, r)
})
}
// GetPort is for herkou deployment
func GetPort() string {
port := os.Getenv("PORT")
if port == "" {
port = "4747"
log.Println("[-] No PORT environment variable detected. Setting to ", port)
}
return ":" + port
}
something like this, or you could just go ahead and use the gorilla mux middleware.