[client] Force interactive login when extending the auth session

A session extend must be answered from the account the peer is registered
under. With a silent PKCE flow (DisablePromptLogin or max_age=0) the IdP
answers from whatever session it already holds, which need not be the
peer's account when several are signed in; the token then fails the
user match in ExtendAuthSession with no way to pick another account.

Mark the PKCE flow request as a session extend so the management server
can force prompt=login for it, overriding the configured silent flow.

client/android/login.go

@@ -199,7 +199,15 @@ type loginHintSetter interface {
 }
 
 func (a *Auth) foregroundGetTokenInfo(authClient *auth.Auth, urlOpener URLOpener, isAndroidTV bool) (*auth.TokenInfo, error) {
-	oAuthFlow, err := authClient.GetOAuthFlow(a.ctx, isAndroidTV)
+	return a.foregroundGetTokenInfoFlow(authClient, urlOpener, isAndroidTV, false)
+}
+
+// foregroundGetTokenInfoFlow runs the interactive flow. sessionExtend tells the
+// server the token will renew this peer's session rather than log a peer in, so
+// it can rule out a silent authorization the IdP could answer from an unrelated
+// account. See PKCEAuthorizationFlowRequest.
+func (a *Auth) foregroundGetTokenInfoFlow(authClient *auth.Auth, urlOpener URLOpener, isAndroidTV bool, sessionExtend bool) (*auth.TokenInfo, error) {
+	oAuthFlow, err := authClient.GetOAuthFlow(a.ctx, isAndroidTV, sessionExtend)
 	if err != nil {
 		return nil, fmt.Errorf("failed to get OAuth flow: %v", err)
 	}

client/android/session.go

@@ -293,11 +293,13 @@ func (c *Client) extendAuthSession(ctx context.Context, urlOpener URLOpener, isA
 	}
 	defer authClient.Close()
 
-	// Passing the config path makes the flow pick up the login_hint: an extend
-	// renews the session of the account already signed in, so it must not stop to
-	// offer a choice.
+	// Passing the config path makes the flow pick up the login_hint. That alone
+	// cannot keep the IdP on this profile's account though — a hint is only a
+	// suggestion, and a silent authorization is answered from whatever session the
+	// IdP already has, which need not be this peer's when several accounts are
+	// signed in. Marking the flow as an extend lets the server rule that out.
 	a := NewAuthWithConfig(ctx, cfg, cfgPath)
-	tokenInfo, err := a.foregroundGetTokenInfo(authClient, urlOpener, isAndroidTV)
+	tokenInfo, err := a.foregroundGetTokenInfoFlow(authClient, urlOpener, isAndroidTV, true)
 	if err != nil {
 		return fmt.Errorf("interactive sso login failed: %v", err)
 	}

client/cmd/login.go

@@ -408,7 +408,7 @@ func foregroundGetTokenInfo(ctx context.Context, cmd *cobra.Command, config *pro
 		hint = profileState.Email
 	}
 
-	oAuthFlow, err := auth.NewOAuthFlow(ctx, config, util.HasGraphicalSession(), false, hint)
+	oAuthFlow, err := auth.NewOAuthFlow(ctx, config, util.HasGraphicalSession(), false, hint, false)
 	if err != nil {
 		return nil, err
 	}

client/internal/auth/auth.go

@@ -103,7 +103,7 @@ func (a *Auth) IsSSOSupported(ctx context.Context) (bool, error) {
 
 	err := a.withRetry(ctx, func(client *mgm.GrpcClient) error {
 		// Try PKCE flow first
-		_, err := a.getPKCEFlow(client)
+		_, err := a.getPKCEFlow(client, false)
 		if err == nil {
 			supportsSSO = true
 			return nil
@@ -138,7 +138,11 @@ func (a *Auth) IsSSOSupported(ctx context.Context) (bool, error) {
 
 // GetOAuthFlow returns an OAuth flow (PKCE or Device) using the existing management connection
 // This avoids creating a new connection to the management server
-func (a *Auth) GetOAuthFlow(ctx context.Context, forceDeviceAuth bool) (OAuthFlow, error) {
+//
+// sessionExtend marks the flow as renewing an existing peer's session rather than
+// logging one in; the server needs it to rule out a silent authorization that the
+// IdP could answer from another account. See PKCEAuthorizationFlowRequest.
+func (a *Auth) GetOAuthFlow(ctx context.Context, forceDeviceAuth bool, sessionExtend bool) (OAuthFlow, error) {
 	var flow OAuthFlow
 	var err error
 
@@ -149,7 +153,7 @@ func (a *Auth) GetOAuthFlow(ctx context.Context, forceDeviceAuth bool) (OAuthFlo
 		}
 
 		// Try PKCE flow first
-		flow, err = a.getPKCEFlow(client)
+		flow, err = a.getPKCEFlow(client, sessionExtend)
 		if err != nil {
 			// If PKCE not supported, try Device flow
 			if s, ok := status.FromError(err); ok && (s.Code() == codes.NotFound || s.Code() == codes.Unimplemented) {
@@ -229,8 +233,8 @@ func (a *Auth) Login(ctx context.Context, setupKey string, jwtToken string) (err
 }
 
 // getPKCEFlow retrieves PKCE authorization flow configuration and creates a flow instance
-func (a *Auth) getPKCEFlow(client *mgm.GrpcClient) (*PKCEAuthorizationFlow, error) {
-	protoFlow, err := client.GetPKCEAuthorizationFlow()
+func (a *Auth) getPKCEFlow(client *mgm.GrpcClient, sessionExtend bool) (*PKCEAuthorizationFlow, error) {
+	protoFlow, err := client.GetPKCEAuthorizationFlow(sessionExtend)
 	if err != nil {
 		if s, ok := status.FromError(err); ok && s.Code() == codes.NotFound {
 			log.Warnf("server couldn't find pkce flow, contact admin: %v", err)

client/internal/auth/oauth.go

@@ -70,12 +70,15 @@ func shouldUseDeviceFlow(force bool, isUnixDesktopClient bool) bool {
 //
 // On Linux distros without desktop environment support, it only tries to initialize the Device Code Flow
 // forceDeviceCodeFlow can be used to skip PKCE and go directly to Device Code Flow (e.g., for Android TV)
-func NewOAuthFlow(ctx context.Context, config *profilemanager.Config, isUnixDesktopClient bool, forceDeviceCodeFlow bool, hint string) (OAuthFlow, error) {
+//
+// sessionExtend marks the flow as renewing an existing peer's session rather than
+// logging one in; see PKCEAuthorizationFlowRequest for what the server makes of it.
+func NewOAuthFlow(ctx context.Context, config *profilemanager.Config, isUnixDesktopClient bool, forceDeviceCodeFlow bool, hint string, sessionExtend bool) (OAuthFlow, error) {
 	if shouldUseDeviceFlow(forceDeviceCodeFlow, isUnixDesktopClient) {
 		return authenticateWithDeviceCodeFlow(ctx, config, hint)
 	}
 
-	pkceFlow, err := authenticateWithPKCEFlow(ctx, config, hint)
+	pkceFlow, err := authenticateWithPKCEFlow(ctx, config, hint, sessionExtend)
 	if err != nil {
 		log.Debugf("failed to initialize pkce authentication with error: %v\n", err)
 		log.Debug("falling back to device code flow")
@@ -85,14 +88,14 @@ func NewOAuthFlow(ctx context.Context, config *profilemanager.Config, isUnixDesk
 }
 
 // authenticateWithPKCEFlow initializes the Proof Key for Code Exchange flow auth flow
-func authenticateWithPKCEFlow(ctx context.Context, config *profilemanager.Config, hint string) (OAuthFlow, error) {
+func authenticateWithPKCEFlow(ctx context.Context, config *profilemanager.Config, hint string, sessionExtend bool) (OAuthFlow, error) {
 	authClient, err := NewAuth(ctx, config.PrivateKey, config.ManagementURL, config)
 	if err != nil {
 		return nil, fmt.Errorf("failed to create auth client: %v", err)
 	}
 	defer authClient.Close()
 
-	pkceFlowInfo, err := authClient.getPKCEFlow(authClient.client)
+	pkceFlowInfo, err := authClient.getPKCEFlow(authClient.client, sessionExtend)
 	if err != nil {
 		return nil, fmt.Errorf("getting pkce authorization flow info failed with error: %v", err)
 	}

client/internal/profilemanager/state.go

@@ -87,10 +87,9 @@ func (pm *ProfileManager) SetActiveProfileState(state *ProfileState) error {
 
 // RemoveProfileState deletes the per-profile state file (which holds the
 // account email used for the SSO login hint and the UI display). Called after
-// profile removal; logout keeps the file so the next login can pass the email
-// as the login_hint. The state file only stores the email, so deleting it is
-// equivalent to clearing it; the next SSO login recreates it. A missing file
-// is not an error.
+// a successful logout so a logged-out profile no longer shows a stale account
+// email. The state file only stores the email, so deleting it is equivalent to
+// clearing it; the next SSO login recreates it. A missing file is not an error.
 func (pm *ProfileManager) RemoveProfileState(profileName string) error {
 	configDir, err := getConfigDir()
 	if err != nil {

client/internal/routemanager/systemops/routeselection_windows_test.go

@@ -1,82 +0,0 @@
-//go:build windows
-
-package systemops
-
-import (
-	"math"
-	"testing"
-
-	"github.com/stretchr/testify/assert"
-)
-
-func TestSortRouteCandidates(t *testing.T) {
-	tests := []struct {
-		name       string
-		candidates []candidateRoute
-		wantOrder  []uint32
-	}{
-		{
-			name: "longest prefix wins over metrics",
-			candidates: []candidateRoute{
-				{interfaceIndex: 1, prefixLength: 0, routeMetric: 0, interfaceMetric: 5},
-				{interfaceIndex: 2, prefixLength: 24, routeMetric: 100, interfaceMetric: 50},
-			},
-			wantOrder: []uint32{2, 1},
-		},
-		{
-			// Windows ranks equal-length prefixes by route metric + interface metric,
-			// so a higher route metric on a low metric interface can still win.
-			name: "combined metric beats route metric alone",
-			candidates: []candidateRoute{
-				{interfaceIndex: 8, prefixLength: 0, routeMetric: 0, interfaceMetric: 100},
-				{interfaceIndex: 5, prefixLength: 0, routeMetric: 10, interfaceMetric: 5},
-			},
-			wantOrder: []uint32{5, 8},
-		},
-		{
-			name: "lower combined metric wins",
-			candidates: []candidateRoute{
-				{interfaceIndex: 5, prefixLength: 0, routeMetric: 300, interfaceMetric: 5},
-				{interfaceIndex: 8, prefixLength: 0, routeMetric: 0, interfaceMetric: 100},
-			},
-			wantOrder: []uint32{8, 5},
-		},
-		{
-			name: "equal combined metric falls back to route metric",
-			candidates: []candidateRoute{
-				{interfaceIndex: 1, prefixLength: 0, routeMetric: 20, interfaceMetric: 10},
-				{interfaceIndex: 2, prefixLength: 0, routeMetric: 5, interfaceMetric: 25},
-			},
-			wantOrder: []uint32{2, 1},
-		},
-		{
-			// The metrics are uint32 on the Windows side, so the sum must not wrap.
-			name: "combined metric beyond the uint32 range",
-			candidates: []candidateRoute{
-				{interfaceIndex: 1, prefixLength: 0, routeMetric: math.MaxUint32, interfaceMetric: 5},
-				{interfaceIndex: 2, prefixLength: 0, routeMetric: math.MaxUint32 - 10, interfaceMetric: 5},
-			},
-			wantOrder: []uint32{2, 1},
-		},
-		{
-			name: "unknown interface metric ranks on route metric only",
-			candidates: []candidateRoute{
-				{interfaceIndex: 1, prefixLength: 0, routeMetric: 30, interfaceMetric: -1},
-				{interfaceIndex: 2, prefixLength: 0, routeMetric: 5, interfaceMetric: 10},
-			},
-			wantOrder: []uint32{2, 1},
-		},
-	}
-
-	for _, tt := range tests {
-		t.Run(tt.name, func(t *testing.T) {
-			sortRouteCandidates(tt.candidates)
-
-			got := make([]uint32, 0, len(tt.candidates))
-			for _, c := range tt.candidates {
-				got = append(got, c.interfaceIndex)
-			}
-			assert.Equal(t, tt.wantOrder, got)
-		})
-	}
-}

client/internal/routemanager/systemops/systemops_windows.go

@@ -882,40 +882,26 @@ func getInterfaceMetric(interfaceIndex uint32, family int16) int {
 	return int(ipInterfaceRow.Metric)
 }
 
-// sortRouteCandidates sorts route candidates by priority: prefix length -> combined metric -> route metric.
-// Windows prefers the longest matching prefix and, among prefixes of the same length, the lowest metric, see
-// https://learn.microsoft.com/en-us/windows-hardware/customize/desktop/unattend/microsoft-windows-tcpip-interfaces-interface-routes-route-metric
+// sortRouteCandidates sorts route candidates by priority: prefix length -> route metric -> interface metric
 func sortRouteCandidates(candidates []candidateRoute) {
 	sort.Slice(candidates, func(i, j int) bool {
 		if candidates[i].prefixLength != candidates[j].prefixLength {
 			return candidates[i].prefixLength > candidates[j].prefixLength
 		}
-		mi, mj := combinedMetric(candidates[i]), combinedMetric(candidates[j])
-		if mi != mj {
-			return mi < mj
+		if candidates[i].routeMetric != candidates[j].routeMetric {
+			return candidates[i].routeMetric < candidates[j].routeMetric
 		}
-		return candidates[i].routeMetric < candidates[j].routeMetric
+		return candidates[i].interfaceMetric < candidates[j].interfaceMetric
 	})
 }
 
-// combinedMetric returns the effective metric Windows uses to rank routes with an equal prefix length:
-// the sum of the route metric and the metric of the interface the route is on, see
-// https://learn.microsoft.com/en-us/windows-server/networking/technologies/network-subsystem/net-sub-interface-metric
-// An unknown interface metric contributes nothing.
-func combinedMetric(candidate candidateRoute) uint64 {
-	if candidate.interfaceMetric < 0 {
-		return uint64(candidate.routeMetric)
-	}
-	return uint64(candidate.routeMetric) + uint64(candidate.interfaceMetric)
-}
-
 // GetBestInterface finds the best interface for reaching a destination,
 // excluding the VPN interface to avoid routing loops.
 //
 // Route selection priority:
 // 1. Longest prefix match (most specific route)
-// 2. Lowest combined metric (route metric + interface metric)
-// 3. Lowest route metric.
+// 2. Lowest route metric
+// 3. Lowest interface metric
 func GetBestInterface(dest netip.Addr, vpnIntf string) (*net.Interface, error) {
 	var skipInterfaceIndex int
 	if vpnIntf != "" {
@@ -939,6 +925,7 @@ func GetBestInterface(dest netip.Addr, vpnIntf string) (*net.Interface, error) {
 		return nil, fmt.Errorf("no route to %s", dest)
 	}
 
+	// Sort routes: prefix length -> route metric -> interface metric
 	sortRouteCandidates(candidates)
 
 	for _, candidate := range candidates {

client/internal/routemanager/systemops/v6route_linux_test.go

@@ -5,7 +5,6 @@ package systemops
 import (
 	"errors"
 	"net"
-	"net/netip"
 	"syscall"
 	"testing"
 
@@ -30,7 +29,6 @@ func ensureIPv6DefaultRoute(t *testing.T) {
 	}
 	if err := netlink.RouteAdd(route); err != nil {
 		if errors.Is(err, syscall.EEXIST) {
-			requireUsableIPv6Nexthop(t)
 			return
 		}
 		t.Skipf("install IPv6 fallback default route: %v", err)
@@ -40,36 +38,4 @@ func ensureIPv6DefaultRoute(t *testing.T) {
 			t.Logf("delete IPv6 fallback default route: %v", err)
 		}
 	})
-
-	requireUsableIPv6Nexthop(t)
-}
-
-// requireUsableIPv6Nexthop skips the test unless the resolved IPv6 default
-// nexthop can actually carry a route. Installing the default route succeeding
-// does not imply the kernel accepts it as a nexthop for a concrete prefix.
-func requireUsableIPv6Nexthop(t *testing.T) {
-	t.Helper()
-
-	nexthop, err := GetNextHop(netip.IPv6Unspecified())
-	if err != nil {
-		t.Skipf("resolve IPv6 default nexthop: %v", err)
-	}
-
-	probe := &netlink.Route{
-		Scope:  netlink.SCOPE_UNIVERSE,
-		Table:  syscall.RT_TABLE_MAIN,
-		Family: netlink.FAMILY_V6,
-		Dst:    &net.IPNet{IP: net.ParseIP("100::64"), Mask: net.CIDRMask(128, 128)},
-	}
-	require.NoError(t, addNextHop(nexthop, probe), "build IPv6 probe route")
-
-	switch err := netlink.RouteAdd(probe); {
-	case err == nil:
-		if err := netlink.RouteDel(probe); err != nil && !errors.Is(err, syscall.ESRCH) {
-			t.Logf("delete IPv6 probe route: %v", err)
-		}
-	case errors.Is(err, syscall.EEXIST):
-	default:
-		t.Skipf("IPv6 nexthop %s unusable for route installation: %v", nexthop, err)
-	}
 }

client/ios/NetBirdSDK/client.go

@@ -429,7 +429,7 @@ func (c *Client) LoginForMobile() string {
 		return fmt.Sprintf("failed to load config: %v", err)
 	}
 
-	oAuthFlow, err := auth.NewOAuthFlow(ctx, cfg, false, false, "")
+	oAuthFlow, err := auth.NewOAuthFlow(ctx, cfg, false, false, "", false)
 	if err != nil {
 		return err.Error()
 	}

client/ios/NetBirdSDK/login.go

@@ -323,7 +323,7 @@ func (a *Auth) login(urlOpener URLOpener, forceDeviceAuth bool, deviceName strin
 const authInfoRequestTimeout = 30 * time.Second
 
 func (a *Auth) foregroundGetTokenInfo(authClient *auth.Auth, urlOpener URLOpener, forceDeviceAuth bool) (*auth.TokenInfo, error) {
-	oAuthFlow, err := authClient.GetOAuthFlow(a.ctx, forceDeviceAuth)
+	oAuthFlow, err := authClient.GetOAuthFlow(a.ctx, forceDeviceAuth, false)
 	if err != nil {
 		return nil, fmt.Errorf("failed to get OAuth flow: %v", err)
 	}

client/server/server.go

@@ -679,7 +679,7 @@ func (s *Server) Login(callerCtx context.Context, msg *proto.LoginRequest) (*pro
 		if msg.Hint != nil {
 			hint = *msg.Hint
 		}
-		oAuthFlow, err := auth.NewOAuthFlow(ctx, config, msg.IsUnixDesktopClient, false, hint)
+		oAuthFlow, err := auth.NewOAuthFlow(ctx, config, msg.IsUnixDesktopClient, false, hint, false)
 		if err != nil {
 			state.Set(internal.StatusLoginFailed)
 			return nil, err
@@ -1724,7 +1724,7 @@ func (s *Server) RequestJWTAuth(
 	}
 
 	// the daemon has no graphical session of its own, only the caller can answer this
-	oAuthFlow, err := auth.NewOAuthFlow(ctx, config, msg.GetHasGraphicalSession(), false, hint)
+	oAuthFlow, err := auth.NewOAuthFlow(ctx, config, msg.GetHasGraphicalSession(), false, hint, false)
 	if err != nil {
 		return nil, gstatus.Errorf(codes.Internal, "failed to create OAuth flow: %v", err)
 	}
@@ -1828,7 +1828,7 @@ func (s *Server) RequestExtendAuthSession(
 	}
 
 	// the daemon has no graphical session of its own, only the caller can answer this
-	oAuthFlow, err := auth.NewOAuthFlow(ctx, config, msg.GetHasGraphicalSession(), false, hint)
+	oAuthFlow, err := auth.NewOAuthFlow(ctx, config, msg.GetHasGraphicalSession(), false, hint, true)
 	if err != nil {
 		return nil, gstatus.Errorf(codes.Internal, "failed to create OAuth flow: %v", err)
 	}

client/ui/authsession/service.go

@@ -6,11 +6,9 @@ import (
 	"context"
 	"time"
 
-	log "github.com/sirupsen/logrus"
 	"google.golang.org/grpc/codes"
 	gstatus "google.golang.org/grpc/status"
 
-	"github.com/netbirdio/netbird/client/internal/profilemanager"
 	"github.com/netbirdio/netbird/client/proto"
 )
 
@@ -62,19 +60,9 @@ func (s *Session) RequestExtend(ctx context.Context, p ExtendStartParams) (Exten
 
 	// a request from the UI implies a graphical session, which the daemon cannot detect itself
 	req := &proto.RequestExtendAuthSessionRequest{HasGraphicalSession: true}
-	hint := p.Hint
-	if hint == "" {
-		pm := profilemanager.NewProfileManager()
-		if active, perr := pm.GetActiveProfile(); perr != nil {
-			log.Debugf("failed to get active profile for login hint: %v", perr)
-		} else if state, serr := pm.GetProfileState(active.ID); serr != nil {
-			log.Debugf("failed to get profile state for login hint: %v", serr)
-		} else {
-			hint = state.Email
-		}
-	}
-	if hint != "" {
-		req.Hint = &hint
+	if p.Hint != "" {
+		h := p.Hint
+		req.Hint = &h
 	}
 
 	resp, err := cli.RequestExtendAuthSession(ctx, req)

client/ui/services/connection.go

@@ -123,16 +123,8 @@ func (s *Connection) Login(ctx context.Context, p LoginParams) (LoginResult, err
 	if p.PreSharedKey != "" {
 		req.OptionalPreSharedKey = ptrStr(p.PreSharedKey)
 	}
-	hint := p.Hint
-	if hint == "" && profileID != "" {
-		if state, serr := profilemanager.NewProfileManager().GetProfileState(profilemanager.ID(profileID)); serr == nil {
-			hint = state.Email
-		} else {
-			log.Debugf("failed to get profile state for login hint: %v", serr)
-		}
-	}
-	if hint != "" {
-		req.Hint = ptrStr(hint)
+	if p.Hint != "" {
+		req.Hint = ptrStr(p.Hint)
 	}
 
 	resp, err := cli.Login(ctx, req)
@@ -236,6 +228,16 @@ func (s *Connection) Logout(ctx context.Context, p LogoutParams) error {
 		return s.classifyDaemonError(err)
 	}
 
+	// The daemon runs as root and can't reach the user-owned per-profile state
+	// file holding the account email (see Profiles.List), so clear the stale
+	// email here; the next SSO login recreates it.
+	if p.ProfileName != "" {
+		if err := profilemanager.NewProfileManager().RemoveProfileState(p.ProfileName); err != nil {
+			// Non-fatal: the logout itself succeeded.
+			log.Warnf("failed to remove profile state for %s: %v", p.ProfileName, err)
+		}
+	}
+
 	return nil
 }
 
@@ -259,7 +261,7 @@ func (s *Connection) waitSSOLogin(ctx context.Context, p WaitSSOParams) (string,
 
 	// Persist the account email the same way the CLI does after its own
 	// WaitSSOLogin: the daemon returns it but cannot store it, since it runs as
-	// root and the per-profile state file is user-owned (see Profiles.List).
+	// root and the per-profile state file is user-owned (see Logout below).
 	// Without this the profile has no email, so Profiles.List shows no account
 	// and later logins and session extends go out without a login_hint —
 	// leaving the IdP to guess which account was meant.

client/ui/services/profile.go

@@ -162,9 +162,8 @@ func (s *Profiles) Remove(ctx context.Context, p ProfileRef) error {
 	}
 
 	// The daemon deletes what it owns but runs as root, so it leaves the
-	// user-owned state file holding the account email behind. Logout keeps the
-	// email on purpose so later logins can pass it as the login_hint; profile
-	// removal is what deletes it. Legacy profiles are keyed by name rather than by a
+	// user-owned state file holding the account email behind (same split as
+	// Connection.Logout). Legacy profiles are keyed by name rather than by a
 	// generated ID, so a recreated profile of the same name would inherit the
 	// deleted one's email and offer it as the login_hint.
 	//

management/internals/shared/grpc/pkce_flow_test.go

@@ -0,0 +1,75 @@
+package grpc
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+
+	"github.com/netbirdio/netbird/shared/management/client/common"
+	"github.com/netbirdio/netbird/shared/management/proto"
+)
+
+func TestApplySessionExtendFlowPolicy(t *testing.T) {
+	tests := []struct {
+		name               string
+		flow               *proto.PKCEAuthorizationFlow
+		sessionExtend      bool
+		disablePromptLogin bool
+		loginFlag          uint32
+	}{
+		{
+			name: "extend forces prompt=login over a silent flow",
+			flow: &proto.PKCEAuthorizationFlow{
+				ProviderConfig: &proto.ProviderConfig{
+					DisablePromptLogin: true,
+					LoginFlag:          uint32(common.LoginFlagMaxAge0),
+				},
+			},
+			sessionExtend:      true,
+			disablePromptLogin: false,
+			loginFlag:          uint32(common.LoginFlagPromptLogin),
+		},
+		{
+			name: "extend replaces max_age=0 so login_hint is honoured",
+			flow: &proto.PKCEAuthorizationFlow{
+				ProviderConfig: &proto.ProviderConfig{
+					DisablePromptLogin: false,
+					LoginFlag:          uint32(common.LoginFlagMaxAge0),
+				},
+			},
+			sessionExtend:      true,
+			disablePromptLogin: false,
+			loginFlag:          uint32(common.LoginFlagPromptLogin),
+		},
+		{
+			name: "login keeps the configured flow untouched",
+			flow: &proto.PKCEAuthorizationFlow{
+				ProviderConfig: &proto.ProviderConfig{
+					DisablePromptLogin: true,
+					LoginFlag:          uint32(common.LoginFlagMaxAge0),
+				},
+			},
+			sessionExtend:      false,
+			disablePromptLogin: true,
+			loginFlag:          uint32(common.LoginFlagMaxAge0),
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			applySessionExtendFlowPolicy(tc.flow, tc.sessionExtend)
+			cfg := tc.flow.GetProviderConfig()
+			assert.Equal(t, tc.disablePromptLogin, cfg.GetDisablePromptLogin())
+			assert.Equal(t, tc.loginFlag, cfg.GetLoginFlag())
+		})
+	}
+}
+
+// A provider config is not guaranteed to be present on the response; clearing
+// the flag must not panic when the validator returned an empty flow.
+func TestApplySessionExtendFlowPolicyWithoutProviderConfig(t *testing.T) {
+	assert.NotPanics(t, func() {
+		applySessionExtendFlowPolicy(&proto.PKCEAuthorizationFlow{}, true)
+		applySessionExtendFlowPolicy(nil, true)
+	})
+}

management/internals/shared/grpc/server.go

@@ -1180,7 +1180,8 @@ func (s *Server) GetPKCEAuthorizationFlow(ctx context.Context, req *proto.Encryp
 		return nil, status.Errorf(codes.Internal, "failed to get server key")
 	}
 
-	err = encryption.DecryptMessage(peerKey, key, req.Body, &proto.PKCEAuthorizationFlowRequest{})
+	flowReq := &proto.PKCEAuthorizationFlowRequest{}
+	err = encryption.DecryptMessage(peerKey, key, req.Body, flowReq)
 	if err != nil {
 		errMSG := fmt.Sprintf("error while decrypting peer's message with Wireguard public key %s.", req.WgPubKey)
 		log.WithContext(ctx).Warn(errMSG)
@@ -1224,6 +1225,7 @@ func (s *Server) GetPKCEAuthorizationFlow(ctx context.Context, req *proto.Encryp
 	}
 
 	flowInfoResp := s.integratedPeerValidator.ValidateFlowResponse(ctx, peerKey.String(), initInfoFlow)
+	applySessionExtendFlowPolicy(flowInfoResp, flowReq.GetSessionExtend())
 
 	encryptedResp, err := encryption.EncryptMessage(peerKey, key, flowInfoResp)
 	if err != nil {
@@ -1236,6 +1238,32 @@ func (s *Server) GetPKCEAuthorizationFlow(ctx context.Context, req *proto.Encryp
 	}, nil
 }
 
+// applySessionExtendFlowPolicy forces a prompt=login flow for a session extend.
+//
+// An extend renews the session of one specific peer, so its token has to come
+// from the account that peer is registered under. A flow that does not prompt
+// leaves the choice to the IdP, which answers a silent authorization from any
+// session it already holds — not necessarily this peer's account when several
+// are signed in, and login_hint is a suggestion the IdP may ignore. The token
+// then fails the jwt.UserID == peer.UserID check in ExtendAuthSession, and the
+// user is given no opportunity to pick a different account.
+//
+// LoginFlagPromptLogin rather than max_age=0: both re-authenticate, but with
+// prompt=login the IdP honours login_hint and offers the peer's own account,
+// whereas max_age=0 leaves the user to find it among every account signed in.
+//
+// Called after ValidateFlowResponse so that a per-peer override cannot reinstate
+// the silent flow for an extend.
+func applySessionExtendFlowPolicy(flow *proto.PKCEAuthorizationFlow, sessionExtend bool) {
+	if !sessionExtend {
+		return
+	}
+	if cfg := flow.GetProviderConfig(); cfg != nil {
+		cfg.DisablePromptLogin = false
+		cfg.LoginFlag = uint32(common.LoginFlagPromptLogin)
+	}
+}
+
 // SyncMeta endpoint is used to synchronize peer's system metadata and notifies the connected,
 // peer's under the same account of any updates.
 func (s *Server) SyncMeta(ctx context.Context, req *proto.EncryptedMessage) (*proto.Empty, error) {

shared/management/client/client.go

@@ -21,7 +21,7 @@ type Client interface {
 	// is not eligible for session extension.
 	ExtendAuthSession(sysInfo *system.Info, jwtToken string) (*proto.ExtendAuthSessionResponse, error)
 	GetDeviceAuthorizationFlow() (*proto.DeviceAuthorizationFlow, error)
-	GetPKCEAuthorizationFlow() (*proto.PKCEAuthorizationFlow, error)
+	GetPKCEAuthorizationFlow(sessionExtend bool) (*proto.PKCEAuthorizationFlow, error)
 	GetServerURL() string
 	// IsHealthy returns the current connection status without blocking.
 	// Used by the engine to monitor connectivity in the background.

shared/management/client/client_test.go

@@ -595,7 +595,12 @@ func Test_GetPKCEAuthorizationFlow(t *testing.T) {
 		},
 	}
 
+	var gotRequest mgmtProto.PKCEAuthorizationFlowRequest
 	mgmtMockServer.GetPKCEAuthorizationFlowFunc = func(ctx context.Context, req *mgmtProto.EncryptedMessage) (*mgmtProto.EncryptedMessage, error) {
+		if err := encryption.DecryptMessage(client.key.PublicKey(), serverKey, req.Body, &gotRequest); err != nil {
+			return nil, err
+		}
+
 		encryptedResp, err := encryption.EncryptMessage(client.key.PublicKey(), serverKey, expectedFlowInfo)
 		if err != nil {
 			return nil, err
@@ -608,11 +613,13 @@ func Test_GetPKCEAuthorizationFlow(t *testing.T) {
 		}, nil
 	}
 
-	flowInfo, err := client.GetPKCEAuthorizationFlow()
+	flowInfo, err := client.GetPKCEAuthorizationFlow(true)
 	if err != nil {
 		t.Error("error while retrieving pkce auth flow information")
 	}
 
+	assert.True(t, gotRequest.GetSessionExtend(), "session extend should reach the server")
+
 	assert.Equal(t, expectedFlowInfo.ProviderConfig.ClientID, flowInfo.ProviderConfig.ClientID, "provider configured client ID should match")
 	assert.Equal(t, expectedFlowInfo.ProviderConfig.ClientSecret, flowInfo.ProviderConfig.ClientSecret, "provider configured client secret should match") //nolint:staticcheck
 }

shared/management/client/grpc.go

@@ -701,7 +701,11 @@ func (c *GrpcClient) GetDeviceAuthorizationFlow() (*proto.DeviceAuthorizationFlo
 
 // GetPKCEAuthorizationFlow returns a pkce authorization flow information.
 // It also takes care of encrypting and decrypting messages.
-func (c *GrpcClient) GetPKCEAuthorizationFlow() (*proto.PKCEAuthorizationFlow, error) {
+//
+// sessionExtend tells the server the flow will renew an existing peer's session
+// rather than log one in, so it can rule out a configuration that would let the
+// IdP answer from an unrelated account. See PKCEAuthorizationFlowRequest.
+func (c *GrpcClient) GetPKCEAuthorizationFlow(sessionExtend bool) (*proto.PKCEAuthorizationFlow, error) {
 	if !c.ready() {
 		return nil, fmt.Errorf("no connection to management in order to get pkce authorization flow")
 	}
@@ -714,7 +718,7 @@ func (c *GrpcClient) GetPKCEAuthorizationFlow() (*proto.PKCEAuthorizationFlow, e
 	mgmCtx, cancel := context.WithTimeout(c.ctx, time.Second*2)
 	defer cancel()
 
-	message := &proto.PKCEAuthorizationFlowRequest{}
+	message := &proto.PKCEAuthorizationFlowRequest{SessionExtend: sessionExtend}
 	encryptedMSG, err := encryption.EncryptMessage(*serverKey, c.key, message)
 	if err != nil {
 		return nil, err

shared/management/client/mock.go

@@ -16,7 +16,7 @@ type MockClient struct {
 	LoginFunc                      func(info *system.Info, sshKey []byte, dnsLabels domain.List) (*proto.LoginResponse, error)
 	ExtendAuthSessionFunc          func(info *system.Info, jwtToken string) (*proto.ExtendAuthSessionResponse, error)
 	GetDeviceAuthorizationFlowFunc func() (*proto.DeviceAuthorizationFlow, error)
-	GetPKCEAuthorizationFlowFunc   func() (*proto.PKCEAuthorizationFlow, error)
+	GetPKCEAuthorizationFlowFunc   func(sessionExtend bool) (*proto.PKCEAuthorizationFlow, error)
 	GetServerURLFunc               func() string
 	HealthCheckFunc                func() error
 	SyncMetaFunc                   func(sysInfo *system.Info) error
@@ -80,11 +80,11 @@ func (m *MockClient) GetDeviceAuthorizationFlow() (*proto.DeviceAuthorizationFlo
 	return m.GetDeviceAuthorizationFlowFunc()
 }
 
-func (m *MockClient) GetPKCEAuthorizationFlow() (*proto.PKCEAuthorizationFlow, error) {
+func (m *MockClient) GetPKCEAuthorizationFlow(sessionExtend bool) (*proto.PKCEAuthorizationFlow, error) {
 	if m.GetPKCEAuthorizationFlowFunc == nil {
 		return nil, nil
 	}
-	return m.GetPKCEAuthorizationFlowFunc()
+	return m.GetPKCEAuthorizationFlowFunc(sessionExtend)
 }
 
 func (m *MockClient) HealthCheck() error {

shared/management/proto/management.proto

@@ -530,8 +530,18 @@ message DeviceAuthorizationFlow {
   }
 }
 
-// PKCEAuthorizationFlowRequest empty struct for future expansion
-message PKCEAuthorizationFlowRequest {}
+// PKCEAuthorizationFlowRequest asks for the PKCE flow configuration to use for
+// an upcoming authorization request.
+message PKCEAuthorizationFlowRequest {
+  // SessionExtend indicates the flow will renew the SSO session of a peer that
+  // is already registered, rather than log in or register one. An extend is
+  // bound to the account that peer belongs to, so the server must not answer it
+  // with a configuration that lets the IdP reply from whatever session is
+  // already active: with several accounts signed in at the IdP that need not be
+  // the peer's own, and the resulting token is rejected as a peer/user mismatch
+  // with no way for the user to correct it.
+  bool SessionExtend = 1;
+}
 
 // PKCEAuthorizationFlow represents Authorization Code Flow information
 // that can be used by the client to login initiate a Oauth 2.0 authorization code grant flow