feat(openid): support logout_hint for RP-initiated logouts

pkg/openid/client/logout.go

@@ -13,12 +13,14 @@ import (
 
 type Logout struct {
 	*Client
-	Cookie            *openid.LogoutCookie
-	logoutCallbackURL string
+	Cookie     *openid.LogoutCookie
+	LogoutHint string
+
+	callbackURL string
 }
 
 func NewLogout(c *Client, r *http.Request) (*Logout, error) {
-	logoutCallbackURL, err := urlpkg.LogoutCallback(r)
+	callbackURL, err := urlpkg.LogoutCallback(r)
 	if err != nil {
 		return nil, fmt.Errorf("generating logout callback url: %w", err)
 	}
@@ -33,21 +35,25 @@ func NewLogout(c *Client, r *http.Request) (*Logout, error) {
 	}
 
 	return &Logout{
-		Client:            c,
-		Cookie:            logoutCookie,
-		logoutCallbackURL: logoutCallbackURL,
+		Client:      c,
+		Cookie:      logoutCookie,
+		LogoutHint:  r.URL.Query().Get("logout_hint"),
+		callbackURL: callbackURL,
 	}, nil
 }
 
 func (in *Logout) SingleLogoutURL(idToken string) string {
 	endSessionEndpoint := in.cfg.Provider().EndSessionEndpointURL()
 	v := endSessionEndpoint.Query()
-	v.Set("post_logout_redirect_uri", in.logoutCallbackURL)
+	v.Set("post_logout_redirect_uri", in.callbackURL)
 	v.Set("state", in.Cookie.State)
 
 	if len(idToken) > 0 {
 		v.Set("id_token_hint", idToken)
 	}
+	if len(in.LogoutHint) > 0 {
+		v.Set("logout_hint", in.LogoutHint)
+	}
 
 	endSessionEndpoint.RawQuery = v.Encode()
 	return endSessionEndpoint.String()

pkg/openid/client/logout_test.go

@@ -70,6 +70,37 @@ func TestLogout_SingleLogoutURL(t *testing.T) {
 		logoutUrl.RawQuery = ""
 		assert.Equal(t, EndSessionEndpoint, logoutUrl.String())
 	})
+
+	t.Run("with logout_hint claim", func(t *testing.T) {
+		logout := newLogout(t)
+		logout.LogoutHint = "some-logout-hint"
+		idToken := ""
+		state := logout.Cookie.State
+
+		raw := logout.SingleLogoutURL(idToken)
+		assert.NotEmpty(t, raw)
+
+		logoutUrl, err := url.Parse(raw)
+		assert.NoError(t, err)
+
+		query := logoutUrl.Query()
+		assert.Len(t, query, 3)
+
+		assert.Contains(t, query, "logout_hint")
+		assert.Equal(t, logout.LogoutHint, query.Get("logout_hint"))
+
+		assert.NotContains(t, query, "id_token_hint")
+		assert.Equal(t, idToken, query.Get("id_token_hint"))
+
+		assert.Contains(t, query, "post_logout_redirect_uri")
+		assert.Equal(t, LogoutCallbackURI, query.Get("post_logout_redirect_uri"))
+
+		assert.Contains(t, query, "state")
+		assert.Equal(t, state, query.Get("state"))
+
+		logoutUrl.RawQuery = ""
+		assert.Equal(t, EndSessionEndpoint, logoutUrl.String())
+	})
 }
 
 func newLogout(t *testing.T) *client.Logout {