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tailscale/cmd/k8s-operator/proxy.go

110 lines
3.3 KiB
Go

// Copyright (c) Tailscale Inc & AUTHORS
// SPDX-License-Identifier: BSD-3-Clause
package main
import (
"context"
"fmt"
"log"
"net/http"
"net/http/httputil"
"net/url"
"os"
"strings"
"tailscale.com/client/tailscale"
"tailscale.com/client/tailscale/apitype"
"tailscale.com/tsnet"
"tailscale.com/types/logger"
)
type whoIsKey struct{}
// authProxy is an http.Handler that authenticates requests using the Tailscale
// LocalAPI and then proxies them to the Kubernetes API.
type authProxy struct {
logf logger.Logf
lc *tailscale.LocalClient
rp *httputil.ReverseProxy
}
func (h *authProxy) ServeHTTP(w http.ResponseWriter, r *http.Request) {
who, err := h.lc.WhoIs(r.Context(), r.RemoteAddr)
if err != nil {
h.logf("failed to authenticate caller: %v", err)
http.Error(w, "failed to authenticate caller", http.StatusInternalServerError)
return
}
r = r.WithContext(context.WithValue(r.Context(), whoIsKey{}, who))
h.rp.ServeHTTP(w, r)
}
// runAuthProxy runs an HTTP server that authenticates requests using the
// Tailscale LocalAPI and then proxies them to the Kubernetes API.
// It listens on :443 and uses the Tailscale HTTPS certificate.
// s will be started if it is not already running.
// rt is used to proxy requests to the Kubernetes API.
//
// It never returns.
func runAuthProxy(s *tsnet.Server, rt http.RoundTripper, logf logger.Logf) {
ln, err := s.ListenTLS("tcp", ":443")
if err != nil {
log.Fatalf("could not listen on :443: %v", err)
}
u, err := url.Parse(fmt.Sprintf("https://%s:%s", os.Getenv("KUBERNETES_SERVICE_HOST"), os.Getenv("KUBERNETES_SERVICE_PORT_HTTPS")))
if err != nil {
log.Fatalf("runAuthProxy: failed to parse URL %v", err)
}
lc, err := s.LocalClient()
if err != nil {
log.Fatalf("could not get local client: %v", err)
}
ap := &authProxy{
logf: logf,
lc: lc,
rp: &httputil.ReverseProxy{
Director: func(r *http.Request) {
// We want to proxy to the Kubernetes API, but we want to use
// the caller's identity to do so. We do this by impersonating
// the caller using the Kubernetes User Impersonation feature:
// https://kubernetes.io/docs/reference/access-authn-authz/authentication/#user-impersonation
// Out of paranoia, remove all authentication headers that might
// have been set by the client.
r.Header.Del("Authorization")
r.Header.Del("Impersonate-Group")
r.Header.Del("Impersonate-User")
r.Header.Del("Impersonate-Uid")
for k := range r.Header {
if strings.HasPrefix(k, "Impersonate-Extra-") {
r.Header.Del(k)
}
}
// Now add the impersonation headers that we want.
who := r.Context().Value(whoIsKey{}).(*apitype.WhoIsResponse)
if who.Node.IsTagged() {
// Use the nodes FQDN as the username, and the nodes tags as the groups.
// "Impersonate-Group" requires "Impersonate-User" to be set.
r.Header.Set("Impersonate-User", strings.TrimSuffix(who.Node.Name, "."))
for _, tag := range who.Node.Tags {
r.Header.Add("Impersonate-Group", tag)
}
} else {
r.Header.Set("Impersonate-User", who.UserProfile.LoginName)
}
// Replace the URL with the Kubernetes APIServer.
r.URL.Scheme = u.Scheme
r.URL.Host = u.Host
},
Transport: rt,
},
}
if err := http.Serve(ln, ap); err != nil {
log.Fatalf("runAuthProxy: failed to serve %v", err)
}
}