diff --git a/workspace-server/internal/middleware/session_auth.go b/workspace-server/internal/middleware/session_auth.go
new file mode 100644
index 00000000..78b9d2ff
--- /dev/null
+++ b/workspace-server/internal/middleware/session_auth.go
@@ -0,0 +1,106 @@
+package middleware
+
+import (
+	"encoding/json"
+	"log"
+	"net/http"
+	"os"
+	"strings"
+	"sync"
+	"time"
+)
+
+// sessionCache holds short-lived positive results for upstream-verified
+// session cookies. Keyed by the raw Cookie header value so ANY change
+// (logout, fresh session) invalidates by just being different bytes.
+//
+// TTL is deliberately short — 30s — because the SaaS session lives on
+// the CP; if ops revokes a token, we want that reflected quickly. A
+// longer TTL would let revoked sessions drift into the tenant. 30s is
+// the sweet spot: fast enough for security, slow enough to avoid CP
+// hammering on every canvas render.
+var sessionCache sync.Map
+
+const sessionCacheTTL = 30 * time.Second
+
+type sessionCacheEntry struct {
+	verifiedAt time.Time
+	ok         bool
+}
+
+// cpSessionEndpointURL is where we verify. Reads the same env the
+// router uses for the /cp/* reverse-proxy. Empty string → feature
+// disabled (self-hosted / dev). Computed at first call so tests can
+// override via env.
+func cpSessionEndpointURL() string {
+	base := strings.TrimRight(os.Getenv("CP_UPSTREAM_URL"), "/")
+	if base == "" {
+		return ""
+	}
+	return base + "/cp/auth/me"
+}
+
+// verifiedCPSession returns true when the request carries a cookie
+// that the CP recognizes as a logged-in user. Caches positive results
+// for sessionCacheTTL so burst canvas renders don't fan out to the CP
+// on every admin fetch.
+//
+// Returns (false, false) when there is no cookie at all — callers
+// distinguish "no credential presented" (fall through to other tiers)
+// from "credential presented but invalid" (abort with 401).
+func verifiedCPSession(cookieHeader string) (valid, presented bool) {
+	if cookieHeader == "" {
+		return false, false
+	}
+	endpoint := cpSessionEndpointURL()
+	if endpoint == "" {
+		return false, true
+	}
+
+	// Cache lookup.
+	if v, ok := sessionCache.Load(cookieHeader); ok {
+		e := v.(sessionCacheEntry)
+		if time.Since(e.verifiedAt) < sessionCacheTTL {
+			return e.ok, true
+		}
+		sessionCache.Delete(cookieHeader)
+	}
+
+	// Fetch /cp/auth/me with the presented cookie. Short timeout —
+	// a slow CP mustn't gate every canvas page render.
+	client := &http.Client{Timeout: 3 * time.Second}
+	req, err := http.NewRequest("GET", endpoint, nil)
+	if err != nil {
+		log.Printf("verifiedCPSession: build req: %v", err)
+		return false, true
+	}
+	req.Header.Set("Cookie", cookieHeader)
+	// Browser-style User-Agent so the CP's bot-detection (if any)
+	// doesn't block us; we're a legitimate proxy for the UI.
+	req.Header.Set("User-Agent", "molecule-tenant-platform/session-verifier")
+
+	resp, err := client.Do(req)
+	if err != nil {
+		log.Printf("verifiedCPSession: upstream: %v", err)
+		return false, true
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK {
+		sessionCache.Store(cookieHeader, sessionCacheEntry{verifiedAt: time.Now(), ok: false})
+		return false, true
+	}
+
+	// Parse minimally to make sure it's actually a session object, not
+	// an HTML error page from an upstream proxy shell.
+	var body struct {
+		UserID string `json:"user_id"`
+	}
+	if err := json.NewDecoder(resp.Body).Decode(&body); err != nil || body.UserID == "" {
+		sessionCache.Store(cookieHeader, sessionCacheEntry{verifiedAt: time.Now(), ok: false})
+		return false, true
+	}
+
+	sessionCache.Store(cookieHeader, sessionCacheEntry{verifiedAt: time.Now(), ok: true})
+	return true, true
+}
diff --git a/workspace-server/internal/middleware/wsauth_middleware.go b/workspace-server/internal/middleware/wsauth_middleware.go
index d0ff090b..9b9a57a7 100644
--- a/workspace-server/internal/middleware/wsauth_middleware.go
+++ b/workspace-server/internal/middleware/wsauth_middleware.go
@@ -123,6 +123,27 @@ func AdminAuth(database *sql.DB) gin.HandlerFunc {
 			}
 		}
 
+		// SaaS-canvas path: when the request carries a WorkOS session
+		// cookie AND the CP confirms it's valid, accept without a
+		// bearer. This is how the tenant's Next.js canvas UI
+		// authenticates — the browser has a session cookie scoped
+		// to .moleculesai.app, and we verify it upstream against
+		// /cp/auth/me (short-cached; see verifiedCPSession).
+		//
+		// Only runs when CP_UPSTREAM_URL is set (prod SaaS); self-
+		// hosted / dev deploys without a CP fall through to the
+		// bearer-only path unchanged.
+		if cookieHeader := c.GetHeader("Cookie"); cookieHeader != "" {
+			if ok, _ := verifiedCPSession(cookieHeader); ok {
+				c.Next()
+				return
+			}
+			// Cookie presented but invalid: fall through to the
+			// bearer-check path, which will 401. We do NOT abort
+			// here so molecli / CLI users with both a cookie and
+			// a stale cookie + valid bearer still pass.
+		}
+
 		// Bearer token is the ONLY accepted credential for admin routes.
 		tok := wsauth.BearerTokenFromHeader(c.GetHeader("Authorization"))
 		if tok == "" {