Add cookie banner REST API with per-banner CORS middleware

Introduce /cookie-banner/v1/{bannerID}/config endpoint for the JS SDK.
The custom CORS middleware validates each request origin against the
specific banner being requested, preventing cross-customer leakage.

Signed-off-by: Émile Ré <emile@getprobo.com>

pkg/server/api/api.go

@@ -28,6 +28,7 @@ import (
 	"go.probo.inc/probo/pkg/accessreview"
 	"go.probo.inc/probo/pkg/baseurl"
 	"go.probo.inc/probo/pkg/connector"
+	"go.probo.inc/probo/pkg/cookiebanner"
 	"go.probo.inc/probo/pkg/esign"
 	"go.probo.inc/probo/pkg/file"
 	"go.probo.inc/probo/pkg/iam"
@@ -36,6 +37,7 @@ import (
 	"go.probo.inc/probo/pkg/securecookie"
 	connect_v1 "go.probo.inc/probo/pkg/server/api/connect/v1"
 	console_v1 "go.probo.inc/probo/pkg/server/api/console/v1"
+	cookiebanner_v1 "go.probo.inc/probo/pkg/server/api/cookiebanner/v1"
 	files_v1 "go.probo.inc/probo/pkg/server/api/files/v1"
 	mcp_v1 "go.probo.inc/probo/pkg/server/api/mcp/v1"
 	slack_v1 "go.probo.inc/probo/pkg/server/api/slack/v1"
@@ -56,6 +58,7 @@ type (
 		AccessReview      *accessreview.Service
 		Slack             *slack.Service
 		Mailman           *mailman.Service
+		CookieBanner      *cookiebanner.Service
 		Cookie            securecookie.Config
 		TokenSecret       string
 		ConnectorRegistry *connector.ConnectorRegistry
@@ -74,6 +77,7 @@ type (
 		csrf                  *http.CrossOriginProtection
 		compliancePageHandler http.Handler
 		consoleHandler        http.Handler
+		cookieBannerHandler   http.Handler
 		filesHandler          http.Handler
 		mcpHandler            http.Handler
 		slackHandler          http.Handler
@@ -135,6 +139,12 @@ func NewServer(cfg Config) (*Server, error) {
 	// POSTs from external identity providers by design.
 	csrf.AddInsecureBypassPattern("POST /connect/v1/saml/2.0/consume")
 
+	// The cookie banner API is called cross-origin from customer websites
+	// by the JS SDK. CORS is handled by the cookie banner middleware.
+	csrf.AddInsecureBypassPattern("GET /cookie-banner/v1/*")
+	csrf.AddInsecureBypassPattern("POST /cookie-banner/v1/*")
+	csrf.AddInsecureBypassPattern("OPTIONS /cookie-banner/v1/*")
+
 	csrf.SetDenyHandler(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		httpserver.RenderJSON(
 			w,
@@ -171,6 +181,10 @@ func NewServer(cfg Config) (*Server, error) {
 			cfg.BaseURL,
 			cfg.CustomDomainCname,
 		),
+		cookieBannerHandler: cookiebanner_v1.NewMux(
+			cfg.Logger.Named("cookiebanner.v1"),
+			cfg.CookieBanner,
+		),
 		filesHandler: files_v1.NewMux(
 			cfg.Logger.Named("files.v1"),
 			cfg.File,
@@ -240,6 +254,7 @@ func (s *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 
 	router.Mount("/console/v1", http.StripPrefix("/console/v1", s.consoleHandler))
 	router.Mount("/connect/v1", http.StripPrefix("/connect/v1", s.connectHandler))
+	router.Mount("/cookie-banner/v1", http.StripPrefix("/cookie-banner/v1", s.cookieBannerHandler))
 	router.Mount("/files/v1", http.StripPrefix("/files/v1", s.filesHandler))
 	router.Mount("/trust/v1", http.StripPrefix("/trust/v1", s.compliancePageHandler))
 	router.Mount("/mcp/v1", http.StripPrefix("/mcp/v1", s.mcpHandler))

pkg/server/api/cookiebanner/v1/cors_middleware.go

@@ -0,0 +1,79 @@
+// Copyright (c) 2026 Probo Inc <hello@getprobo.com>.
+//
+// Permission to use, copy, modify, and/or distribute this software for any
+// purpose with or without fee is hereby granted, provided that the above
+// copyright notice and this permission notice appear in all copies.
+//
+// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+// REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+// AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+// INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+// LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+// OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+// PERFORMANCE OF THIS SOFTWARE.
+
+package cookiebanner_v1
+
+import (
+	"errors"
+	"net/http"
+
+	"github.com/go-chi/chi/v5"
+	"go.gearno.de/kit/log"
+	"go.probo.inc/probo/pkg/cookiebanner"
+	"go.probo.inc/probo/pkg/gid"
+)
+
+func newCORSMiddleware(logger *log.Logger, cookieBannerSvc *cookiebanner.Service) func(http.Handler) http.Handler {
+	return func(next http.Handler) http.Handler {
+		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			origin := r.Header.Get("Origin")
+			if origin == "" {
+				next.ServeHTTP(w, r)
+				return
+			}
+
+			bannerIDStr := chi.URLParam(r, "bannerID")
+			if bannerIDStr == "" {
+				http.Error(w, "forbidden", http.StatusForbidden)
+				return
+			}
+
+			bannerID, err := gid.ParseGID(bannerIDStr)
+			if err != nil {
+				http.Error(w, "forbidden", http.StatusForbidden)
+				return
+			}
+
+			banner, err := cookieBannerSvc.GetActiveCookieBanner(r.Context(), bannerID)
+			if err != nil {
+				if errors.Is(err, cookiebanner.ErrBannerNotFound) {
+					http.Error(w, "forbidden", http.StatusForbidden)
+					return
+				}
+				logger.ErrorCtx(r.Context(), "cannot load cookie banner for CORS check", log.Error(err))
+				http.Error(w, "internal server error", http.StatusInternalServerError)
+				return
+			}
+
+			canonicalOrigin := cookiebanner.CanonicalizeOrigin(origin)
+			if banner.Origin != canonicalOrigin {
+				http.Error(w, "forbidden", http.StatusForbidden)
+				return
+			}
+
+			w.Header().Set("Access-Control-Allow-Origin", origin)
+			w.Header().Set("Access-Control-Allow-Methods", "GET, POST, OPTIONS")
+			w.Header().Set("Access-Control-Allow-Headers", "Content-Type")
+			w.Header().Set("Access-Control-Max-Age", "600")
+			w.Header().Set("Vary", "Origin")
+
+			if r.Method == http.MethodOptions {
+				w.WriteHeader(http.StatusNoContent)
+				return
+			}
+
+			next.ServeHTTP(w, r)
+		})
+	}
+}

pkg/server/api/cookiebanner/v1/handler.go

@@ -0,0 +1,49 @@
+// Copyright (c) 2026 Probo Inc <hello@getprobo.com>.
+//
+// Permission to use, copy, modify, and/or distribute this software for any
+// purpose with or without fee is hereby granted, provided that the above
+// copyright notice and this permission notice appear in all copies.
+//
+// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+// REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+// AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+// INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+// LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+// OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+// PERFORMANCE OF THIS SOFTWARE.
+
+package cookiebanner_v1
+
+import (
+	"net/http"
+
+	"github.com/go-chi/chi/v5"
+	"go.gearno.de/kit/httpserver"
+	"go.gearno.de/kit/log"
+	"go.probo.inc/probo/pkg/cookiebanner"
+)
+
+type Handler struct {
+	logger          *log.Logger
+	cookieBannerSvc *cookiebanner.Service
+}
+
+func NewMux(
+	logger *log.Logger,
+	cookieBannerSvc *cookiebanner.Service,
+) *chi.Mux {
+	h := &Handler{
+		logger:          logger,
+		cookieBannerSvc: cookieBannerSvc,
+	}
+
+	r := chi.NewMux()
+	r.Use(newCORSMiddleware(logger, cookieBannerSvc))
+	r.Get("/{bannerID}/config", h.handleGetConfig)
+
+	return r
+}
+
+func (h *Handler) handleGetConfig(w http.ResponseWriter, r *http.Request) {
+	httpserver.RenderJSON(w, http.StatusOK, map[string]string{"status": "ok"})
+}