feat: fallback to SameSite Lax mode if cookie is not secure (#1105)

Also, will allow to set cookie `SameSite` mode on command line or
environment. Note that `None` mode will be forced to ``Lax`` if
cookie is set to not be secure.

Signed-off-by: Valentin Lab <valentin.lab@kalysto.org>

lib/anubis_test.go

@@ -299,6 +299,7 @@ func TestCookieSettings(t *testing.T) {
 		CookieDomain:      "127.0.0.1",
 		CookiePartitioned: true,
 		CookieSecure:      true,
+		CookieSameSite:    http.SameSiteNoneMode,
 		CookieExpiration:  anubis.CookieDefaultExpirationTime,
 	})
 
@@ -339,6 +340,65 @@ func TestCookieSettings(t *testing.T) {
 	if ckie.Secure != srv.opts.CookieSecure {
 		t.Errorf("wanted secure flag %v, got: %v", srv.opts.CookieSecure, ckie.Secure)
 	}
+	if ckie.SameSite != srv.opts.CookieSameSite {
+		t.Errorf("wanted same site option %v, got: %v", srv.opts.CookieSameSite, ckie.SameSite)
+	}
+}
+
+func TestCookieSettingsSameSiteNoneModeDowngradedToLaxWhenUnsecure(t *testing.T) {
+	pol := loadPolicies(t, "testdata/zero_difficulty.yaml", 0)
+
+	srv := spawnAnubis(t, Options{
+		Next:   http.NewServeMux(),
+		Policy: pol,
+
+		CookieDomain:      "127.0.0.1",
+		CookiePartitioned: true,
+		CookieSecure:      false,
+		CookieSameSite:    http.SameSiteNoneMode,
+		CookieExpiration:  anubis.CookieDefaultExpirationTime,
+	})
+
+	ts := httptest.NewServer(internal.RemoteXRealIP(true, "tcp", srv))
+	defer ts.Close()
+
+	cli := httpClient(t)
+	chall := makeChallenge(t, ts, cli)
+
+	resp := handleChallengeZeroDifficulty(t, ts, cli, chall)
+
+	if resp.StatusCode != http.StatusFound {
+		resp.Write(os.Stderr)
+		t.Errorf("wanted %d, got: %d", http.StatusFound, resp.StatusCode)
+	}
+
+	var ckie *http.Cookie
+	for _, cookie := range resp.Cookies() {
+		t.Logf("%#v", cookie)
+		if cookie.Name == anubis.CookieName {
+			ckie = cookie
+			break
+		}
+	}
+	if ckie == nil {
+		t.Errorf("Cookie %q not found", anubis.CookieName)
+		return
+	}
+
+	if ckie.Domain != "127.0.0.1" {
+		t.Errorf("cookie domain is wrong, wanted 127.0.0.1, got: %s", ckie.Domain)
+	}
+
+	if ckie.Partitioned != srv.opts.CookiePartitioned {
+		t.Errorf("wanted partitioned flag %v, got: %v", srv.opts.CookiePartitioned, ckie.Partitioned)
+	}
+
+	if ckie.Secure != srv.opts.CookieSecure {
+		t.Errorf("wanted secure flag %v, got: %v", srv.opts.CookieSecure, ckie.Secure)
+	}
+	if ckie.SameSite != http.SameSiteLaxMode {
+		t.Errorf("wanted same site Lax option %v, got: %v", http.SameSiteLaxMode, ckie.SameSite)
+	}
 }
 
 func TestCheckDefaultDifficultyMatchesPolicy(t *testing.T) {

lib/config.go

@@ -43,6 +43,7 @@ type Options struct {
 	OpenGraph            config.OpenGraph
 	ServeRobotsTXT       bool
 	CookieSecure         bool
+	CookieSameSite       http.SameSite
 	Logger               *slog.Logger
 	PublicUrl            string
 	JWTRestrictionHeader string

lib/http.go

@@ -56,6 +56,8 @@ func (s *Server) SetCookie(w http.ResponseWriter, cookieOpts CookieOpts) {
 	var domain = s.opts.CookieDomain
 	var name = anubis.CookieName
 	var path = "/"
+	var sameSite = s.opts.CookieSameSite
+
 	if cookieOpts.Name != "" {
 		name = cookieOpts.Name
 	}
@@ -72,11 +74,15 @@ func (s *Server) SetCookie(w http.ResponseWriter, cookieOpts CookieOpts) {
 		cookieOpts.Expiry = s.opts.CookieExpiration
 	}
 
+	if s.opts.CookieSameSite == http.SameSiteNoneMode && !s.opts.CookieSecure {
+		sameSite = http.SameSiteLaxMode
+	}
+
 	http.SetCookie(w, &http.Cookie{
 		Name:        name,
 		Value:       cookieOpts.Value,
 		Expires:     time.Now().Add(cookieOpts.Expiry),
-		SameSite:    http.SameSiteNoneMode,
+		SameSite:    sameSite,
 		Domain:      domain,
 		Secure:      s.opts.CookieSecure,
 		Partitioned: s.opts.CookiePartitioned,
@@ -88,6 +94,8 @@ func (s *Server) ClearCookie(w http.ResponseWriter, cookieOpts CookieOpts) {
 	var domain = s.opts.CookieDomain
 	var name = anubis.CookieName
 	var path = "/"
+	var sameSite = s.opts.CookieSameSite
+
 	if cookieOpts.Name != "" {
 		name = cookieOpts.Name
 	}
@@ -99,13 +107,16 @@ func (s *Server) ClearCookie(w http.ResponseWriter, cookieOpts CookieOpts) {
 			domain = etld
 		}
 	}
+	if s.opts.CookieSameSite == http.SameSiteNoneMode && !s.opts.CookieSecure {
+		sameSite = http.SameSiteLaxMode
+	}
 
 	http.SetCookie(w, &http.Cookie{
 		Name:        name,
 		Value:       "",
 		MaxAge:      -1,
 		Expires:     time.Now().Add(-1 * time.Minute),
-		SameSite:    http.SameSiteNoneMode,
+		SameSite:    sameSite,
 		Partitioned: s.opts.CookiePartitioned,
 		Domain:      domain,
 		Secure:      s.opts.CookieSecure,