From fc5c0e27892bfac432dae91655b4c320a46ecdf1 Mon Sep 17 00:00:00 2001
From: Jens Langhammer <jens@goauthentik.io>
Date: Thu, 15 May 2025 12:32:27 +0200
Subject: [PATCH] generate MPPE key

Signed-off-by: Jens Langhammer <jens@goauthentik.io>
---
 internal/outpost/radius/eap/handler.go        |  7 ++--
 internal/outpost/radius/eap/protocol/empty.go |  3 ++
 internal/outpost/radius/eap/tls/payload.go    | 37 ++++++++++++++++---
 internal/outpost/radius/eap/tls/state.go      |  1 +
 4 files changed, 39 insertions(+), 9 deletions(-)

diff --git a/internal/outpost/radius/eap/handler.go b/internal/outpost/radius/eap/handler.go
index 0e2558ae42..f05ff37324 100644
--- a/internal/outpost/radius/eap/handler.go
+++ b/internal/outpost/radius/eap/handler.go
@@ -32,12 +32,11 @@ func (p *Packet) Handle(stm StateManager, w radius.ResponseWriter, r *radius.Pac
 	stm.SetEAPState(rst, newState)
 
 	rres := r.Response(radius.CodeAccessChallenge)
-	if _, ok := res.Payload.(protocol.EmptyPayload); ok {
+	if p, ok := res.Payload.(protocol.EmptyPayload); ok {
+		// This is a bit hacky here
 		res.code = CodeSuccess
-		rres.Code = radius.CodeAccessAccept
 		res.id -= 1
-		rfc2865.UserName_SetString(rres, "foo")
-		rfc2865.FramedMTU_Set(rres, rfc2865.FramedMTU(1400))
+		rres = p.ModifyPacket(rres)
 	}
 	rfc2865.State_SetString(rres, rst)
 	eapEncoded, err := res.Encode()
diff --git a/internal/outpost/radius/eap/protocol/empty.go b/internal/outpost/radius/eap/protocol/empty.go
index e92e8a6b01..05ee0ffd39 100644
--- a/internal/outpost/radius/eap/protocol/empty.go
+++ b/internal/outpost/radius/eap/protocol/empty.go
@@ -1,6 +1,9 @@
 package protocol
 
+import "layeh.com/radius"
+
 type EmptyPayload struct {
+	ModifyPacket func(p *radius.Packet) *radius.Packet
 }
 
 func (ep EmptyPayload) Decode(raw []byte) error {
diff --git a/internal/outpost/radius/eap/tls/payload.go b/internal/outpost/radius/eap/tls/payload.go
index 4c9951ee77..59847d3e3f 100644
--- a/internal/outpost/radius/eap/tls/payload.go
+++ b/internal/outpost/radius/eap/tls/payload.go
@@ -11,6 +11,8 @@ import (
 	log "github.com/sirupsen/logrus"
 	"goauthentik.io/internal/outpost/radius/eap/debug"
 	"goauthentik.io/internal/outpost/radius/eap/protocol"
+	"layeh.com/radius"
+	"layeh.com/radius/vendors/microsoft"
 )
 
 const maxChunkSize = 1000
@@ -106,7 +108,7 @@ func (p *Payload) Handle(stt any) (protocol.Payload, *State) {
 				return
 			}
 			log.Debug("TLS: handshake done")
-			st.HandshakeDone = true
+			p.handshakeFinished(st)
 		}()
 	} else if len(p.Data) > 0 {
 		log.Debug("TLS: Updating buffer with new TLS data from packet")
@@ -135,12 +137,37 @@ func (p *Payload) Handle(stt any) (protocol.Payload, *State) {
 		return p.sendNextChunk(st)
 	}
 	if st.Conn.writer.Len() == 0 && st.HandshakeDone {
-		return protocol.EmptyPayload{}, st
+		return protocol.EmptyPayload{
+			ModifyPacket: func(p *radius.Packet) *radius.Packet {
+				p.Code = radius.CodeAccessAccept
+				microsoft.MSMPPERecvKey_Set(p, st.MPPEKey[:32])
+				return p
+			},
+		}, st
 	}
-	if len(st.Conn.OutboundData()) > 0 {
-		return p.startChunkedTransfer(st.Conn.OutboundData(), st)
+	return p.startChunkedTransfer(st.Conn.OutboundData(), st)
+}
+
+func (p *Payload) handshakeFinished(st *State) {
+	cs := st.TLS.ConnectionState()
+	label := "client EAP encryption"
+	var context []byte
+	switch cs.Version {
+	case tls.VersionTLS10:
+		log.Debugf("TLS: Version %d (1.0)", cs.Version)
+	case tls.VersionTLS11:
+		log.Debugf("TLS: Version %d (1.1)", cs.Version)
+	case tls.VersionTLS12:
+		log.Debugf("TLS: Version %d (1.2)", cs.Version)
+	case tls.VersionTLS13:
+		log.Debugf("TLS: Version %d (1.3)", cs.Version)
+		label = "EXPORTER_EAP_TLS_Key_Material"
+		context = []byte{13}
 	}
-	panic("we shouldn't get here")
+	ksm, err := cs.ExportKeyingMaterial(label, context, 64+64)
+	log.Debugf("TLS: ksm % x %v", ksm, err)
+	st.MPPEKey = ksm
+	st.HandshakeDone = true
 }
 
 func (p *Payload) startChunkedTransfer(data []byte, st *State) (*Payload, *State) {
diff --git a/internal/outpost/radius/eap/tls/state.go b/internal/outpost/radius/eap/tls/state.go
index 6470d6d3a0..883349a1f8 100644
--- a/internal/outpost/radius/eap/tls/state.go
+++ b/internal/outpost/radius/eap/tls/state.go
@@ -10,6 +10,7 @@ type State struct {
 	RemainingChunks  [][]byte
 	HandshakeDone    bool
 	ClientHello      *tls.ClientHelloInfo
+	MPPEKey          []byte
 	TotalPayloadSize int
 	TLS              *tls.Conn
 	Conn             *TLSConnection