root: check remote IP for proxy protocol same as HTTP/etc (#12094)

Signed-off-by: Jens Langhammer <jens@goauthentik.io>

internal/utils/proxy.go

@@ -0,0 +1,34 @@
+package utils
+
+import (
+	"net"
+
+	"github.com/pires/go-proxyproto"
+	log "github.com/sirupsen/logrus"
+	"goauthentik.io/internal/config"
+)
+
+func GetProxyConnectionPolicy() proxyproto.ConnPolicyFunc {
+	nets := []*net.IPNet{}
+	for _, rn := range config.Get().Listen.TrustedProxyCIDRs {
+		_, cidr, err := net.ParseCIDR(rn)
+		if err != nil {
+			continue
+		}
+		nets = append(nets, cidr)
+	}
+	return func(connPolicyOptions proxyproto.ConnPolicyOptions) (proxyproto.Policy, error) {
+		host, _, err := net.SplitHostPort(connPolicyOptions.Upstream.String())
+		if err == nil {
+			// remoteAddr will be nil if the IP cannot be parsed
+			remoteAddr := net.ParseIP(host)
+			for _, allowedCidr := range nets {
+				if remoteAddr != nil && allowedCidr.Contains(remoteAddr) {
+					log.WithField("remoteAddr", remoteAddr).WithField("cidr", allowedCidr.String()).Trace("Using remote IP from proxy protocol")
+					return proxyproto.USE, nil
+				}
+			}
+		}
+		return proxyproto.SKIP, nil
+	}
+}