[client] Verify the SSO login came back for the hinted account

login_hint is a suggestion the IdP may ignore: with a silent flow configured (DisablePromptLogin or max_age=0) and a live IdP session for another account, the login completes with that account's token. On a registered peer the management server rejects it as a user mismatch, but on a fresh profile the peer silently registers under the wrong account and the profile is then bound to it — every later login follows the stored hint straight back. After the token exchange, compare the ID token's email against the hint the flow was sent with. On a mismatch, do not log in to management with the token; run one more round asking the IdP to re-decide the account (prompt=login, via ForceAccountPrompt — DisablePromptLogin still wins there). If the prompted round also comes back different, proceed with a warning: the address may legitimately have changed, and refusing forever would lock the user out of the profile while the management server still rejects a token that does not own the peer. A token or profile with no email to compare is not judged. The retry differs per platform because of who opens the browser: - CLI (netbird login foreground) and Android run the whole flow in one process, so the mismatch retries automatically: the browser reopens with the account prompt within the same login attempt. - On desktop the login is split between the daemon and the GUI: Login hands the authorize URL to the GUI, WaitSSOLogin blocks for the token, and only the GUI can open a browser. A new URL cannot be handed out from inside WaitSSOLogin (its response has no field for one, kept that way to avoid a proto change), so the daemon arms forceAccountPrompt, fails the round with "connect again to choose the account", and builds the next Login's flow with the prompt — the user's next connect is the retry. The flag and the flow annotations live in daemon memory only; SwitchProfile drops them so the previous profile's hint cannot judge the next profile's token. The device code flow has no prompt parameter (RFC 8628), so a prompted round there runs as-is and a repeated mismatch is let through with the warning rather than looping.
2026-09-17 04:09:07 +02:00 · 2026-08-18 10:51:05 +02:00
parent bfa5d0e1f3
commit 907e66b9d7
7 changed files with 436 additions and 26 deletions
@@ -0,0 +1,104 @@
+package auth
+
+import (
+	"encoding/base64"
+	"encoding/json"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestTokenInfoMatchesAccount(t *testing.T) {
+	tests := []struct {
+		name  string
+		token TokenInfo
+		hint  string
+		match bool
+	}{
+		{
+			name:  "same account",
+			token: TokenInfo{Email: "user@example.com"},
+			hint:  "user@example.com",
+			match: true,
+		},
+		{
+			name:  "different account",
+			token: TokenInfo{Email: "other@example.com"},
+			hint:  "user@example.com",
+			match: false,
+		},
+		{
+			name:  "case differences are the same account",
+			token: TokenInfo{Email: "User@Example.com"},
+			hint:  "user@example.com",
+			match: true,
+		},
+		{
+			name:  "no hint leaves the choice to the IdP",
+			token: TokenInfo{Email: "other@example.com"},
+			hint:  "",
+			match: true,
+		},
+		{
+			name:  "token without an email is not judged",
+			token: TokenInfo{Email: ""},
+			hint:  "user@example.com",
+			match: true,
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			assert.Equal(t, tc.match, tc.token.MatchesAccount(tc.hint))
+		})
+	}
+}
+
+func TestParseEmailFromIDToken(t *testing.T) {
+	tests := []struct {
+		name      string
+		claims    map[string]interface{}
+		wantValue string
+		wantErr   bool
+	}{
+		{
+			name:      "email claim",
+			claims:    map[string]interface{}{"email": "user@example.com", "name": "Some One"},
+			wantValue: "user@example.com",
+		},
+		{
+			name:      "name fallback",
+			claims:    map[string]interface{}{"name": "Some One"},
+			wantValue: "Some One",
+		},
+		{
+			name:    "neither claim present",
+			claims:  map[string]interface{}{"sub": "abc"},
+			wantErr: true,
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			value, err := parseEmailFromIDToken(idTokenWithClaims(t, tc.claims))
+			if tc.wantErr {
+				require.Error(t, err)
+				return
+			}
+			require.NoError(t, err)
+			assert.Equal(t, tc.wantValue, value)
+		})
+	}
+}
+
+func TestRetryFlowForAccountUnsupportedFlow(t *testing.T) {
+	assert.Nil(t, RetryFlowForAccount(&DeviceAuthorizationFlow{}))
+}
+
+func idTokenWithClaims(t *testing.T, claims map[string]interface{}) string {
+	t.Helper()
+	payload, err := json.Marshal(claims)
+	require.NoError(t, err)
+	return "header." + base64.RawURLEncoding.EncodeToString(payload) + ".signature"
+}
@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"net/http"
 	"runtime"
+	"strings"

 	log "github.com/sirupsen/logrus"
 	"google.golang.org/grpc/codes"
@@ -25,6 +26,14 @@ type HTTPClient interface {
 	Do(req *http.Request) (*http.Response, error)
 }

+// accountPromptForcer is implemented by the PKCE flow only. The device code
+// flow has no equivalent: RFC 8628 defines no prompt parameter, and the user
+// confirms the code on a page that shows which account signs in, so a silent
+// wrong-account answer is not the failure mode there.
+type accountPromptForcer interface {
+	ForceAccountPrompt()
+}
+
 // AuthFlowInfo holds information for the OAuth 2.0  authorization flow
 type AuthFlowInfo struct { //nolint:revive
 	DeviceCode              string `json:"device_code"`
@@ -51,6 +60,22 @@ type TokenInfo struct {
 	Email        string `json:"-"`
 }

+// MatchesAccount reports whether the token belongs to the account a profile is
+// bound to. A hint the IdP could not have acted on — no hint stored, or a token
+// that carried no email — is reported as a match: the check exists to catch a
+// login answered from the wrong account, not to block one it cannot judge.
+//
+// The comparison is case-insensitive. Local-parts are case-sensitive per RFC
+// 5321, but no IdP in practice issues two accounts differing only in case, and
+// an IdP that echoes a differently-cased address would otherwise fail every
+// login.
+func (t TokenInfo) MatchesAccount(hint string) bool {
+	if hint == "" || t.Email == "" {
+		return true
+	}
+	return strings.EqualFold(t.Email, hint)
+}
+
 // GetTokenToUse returns either the access or id token based on UseIDToken field
 func (t TokenInfo) GetTokenToUse() string {
 	if t.UseIDToken {
@@ -136,3 +161,21 @@ func authenticateWithDeviceCodeFlow(ctx context.Context, config *profilemanager.

 	return deviceFlowInfo, nil
 }
+
+// RetryFlowForAccount returns a flow that asks the IdP to re-authenticate, for
+// a login answered with an account other than the one hinted. Returns nil when
+// the flow cannot ask — the caller then proceeds with the token it has.
+//
+// Proceeding rather than failing is deliberate. The hint is an email that may
+// simply have changed since it was stored, and refusing the login would lock a
+// user out of their own profile over a rename. The retry gives the account a
+// chance to be corrected; the server still rejects a token that does not own
+// the peer.
+func RetryFlowForAccount(flow OAuthFlow) OAuthFlow {
+	forcer, ok := flow.(accountPromptForcer)
+	if !ok {
+		return nil
+	}
+	forcer.ForceAccountPrompt()
+	return flow
+}
@@ -87,10 +87,11 @@ func validatePKCEConfig(config *PKCEAuthProviderConfig) error {
 // PKCEAuthorizationFlow implements the OAuthFlow interface for
 // the Authorization Code Flow with PKCE.
 type PKCEAuthorizationFlow struct {
-	providerConfig PKCEAuthProviderConfig
-	state          string
-	codeVerifier   string
-	oAuthConfig    *oauth2.Config
+	providerConfig     PKCEAuthProviderConfig
+	state              string
+	codeVerifier       string
+	oAuthConfig        *oauth2.Config
+	forceAccountPrompt bool
 }

 // NewPKCEAuthorizationFlow returns new PKCE authorization code flow.
@@ -154,10 +155,12 @@ func (p *PKCEAuthorizationFlow) RequestAuthInfo(ctx context.Context) (AuthFlowIn
 		oauth2.SetAuthURLParam("audience", p.providerConfig.Audience),
 	}
 	if !p.providerConfig.DisablePromptLogin {
-		switch p.providerConfig.LoginFlag {
-		case common.LoginFlagPromptLogin:
+		switch {
+		case p.forceAccountPrompt:
 			params = append(params, oauth2.SetAuthURLParam("prompt", "login"))
-		case common.LoginFlagMaxAge0:
+		case p.providerConfig.LoginFlag == common.LoginFlagPromptLogin:
+			params = append(params, oauth2.SetAuthURLParam("prompt", "login"))
+		case p.providerConfig.LoginFlag == common.LoginFlagMaxAge0:
 			params = append(params, oauth2.SetAuthURLParam("max_age", "0"))
 		}
 	}
@@ -178,6 +181,17 @@ func (p *PKCEAuthorizationFlow) SetLoginHint(hint string) {
 	p.providerConfig.LoginHint = hint
 }

+// ForceAccountPrompt makes the next authorization request ask the IdP to
+// re-authenticate instead of answering from the session it already holds. Used
+// to retry a login that came back for an account other than the one hinted.
+//
+// DisablePromptLogin still wins: it is set for IdPs that break on prompt=login,
+// where retrying with it would replace a wrong-account login with one that
+// cannot complete at all.
+func (p *PKCEAuthorizationFlow) ForceAccountPrompt() {
+	p.forceAccountPrompt = true
+}
+
 // WaitToken waits for the OAuth token in the PKCE Authorization Flow.
 // It starts an HTTP server to receive the OAuth token callback and waits for the token or an error.
 // Once the token is received, it is converted to TokenInfo and validated before returning.
@@ -321,10 +335,10 @@ func (p *PKCEAuthorizationFlow) parseOAuthToken(token *oauth2.Token) (TokenInfo,
 }

 // parseEmailFromIDToken extracts the email (or name) claim from an ID token
-// without verifying its signature. The value is best-effort and used only as a
-// UX convenience (login hint prefill and display); it never drives an
-// authorization decision. The authoritative identity is established server-side
-// from the signature-verified token.
+// without verifying its signature. The value is best-effort: it prefills the
+// login hint, is displayed, and is compared against the account a profile is
+// bound to (see MatchesAccount). It never grants anything — the authoritative
+// identity is established server-side from the signature-verified token.
 func parseEmailFromIDToken(token string) (string, error) {
 	parts := strings.Split(token, ".")
 	if len(parts) < 2 {
@@ -340,19 +354,14 @@ func parseEmailFromIDToken(token string) (string, error) {
 		return "", fmt.Errorf("json unmarshal error: %w", err)
 	}

-	var email string
-	if emailValue, ok := claims["email"].(string); ok {
-		email = emailValue
-	} else {
-		val, ok := claims["name"].(string)
-		if ok {
-			email = val
-		} else {
-			return "", fmt.Errorf("email or name field not found in token payload")
-		}
+	if email, ok := claims["email"].(string); ok {
+		return email, nil
+	}
+	if name, ok := claims["name"].(string); ok {
+		return name, nil
 	}

-	return email, nil
+	return "", fmt.Errorf("email or name field not found in token payload")
 }

 func createCodeChallenge(codeVerifier string) string {