dream: signed session cookies (tamper-evident sid) + 11 tests

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/dream/session.sx

@@ -72,6 +72,48 @@
   dream-drop-cookie
   (fn (resp name) (dream-set-cookie resp name "" {:max-age 0})))
 
+;; ── signed cookie values (tamper-evident) ──────────────────────────
+;; NOTE: pure-SX keyed hash — not cryptographic; production should inject a host
+;; HMAC. Value carries no "." so the first "." splits value from signature.
+(define
+  dr/sess-hash
+  (fn (s) (dr/sess-hash-loop s 0 (string-length s) 7)))
+(define
+  dr/sess-hash-loop
+  (fn
+    (s i n h)
+    (if
+      (>= i n)
+      h
+      (dr/sess-hash-loop
+        s
+        (+ i 1)
+        n
+        (mod (+ (* h 131) (char-code (char-at s i))) 2147483647)))))
+(define
+  dr/sess-sig
+  (fn (secret val) (str (dr/sess-hash (str secret "|" val)))))
+
+(define
+  dream-cookie-sign
+  (fn (secret val) (str val "." (dr/sess-sig secret val))))
+(define
+  dream-cookie-unsign
+  (fn
+    (secret signed)
+    (if
+      (or (nil? signed) (= signed ""))
+      nil
+      (let
+        ((dot (index-of signed ".")))
+        (if
+          (< dot 0)
+          nil
+          (let
+            ((val (substr signed 0 dot))
+              (sig (substr signed (+ dot 1))))
+            (if (= sig (dr/sess-sig secret val)) val nil)))))))
+
 ;; ── in-memory session store (tests + demos) ────────────────────────
 ;; A backend is (fn (op) result) where op is a dict {:op ... :sid ... :key ...}.
 (define
@@ -143,6 +185,32 @@
                     sid
                     {:path "/" :http-only true :same-site "Lax"}))))))))))
 
+;; signed variant: the cookie value is signed so a guessed/forged sid is rejected
+(define
+  dream-sessions-signed
+  (fn
+    (backend secret)
+    (fn
+      (next)
+      (fn
+        (req)
+        (let
+          ((sid0 (dream-cookie-unsign secret (dream-cookie req dream-session-cookie-name))))
+          (let
+            ((have (and sid0 (backend {:op "session/exists" :sid sid0}))))
+            (let
+              ((sid (if have sid0 (backend {:op "session/create"}))))
+              (let
+                ((resp (next (assoc req :dream-session {:io backend :sid sid}))))
+                (if
+                  have
+                  resp
+                  (dream-set-cookie
+                    resp
+                    dream-session-cookie-name
+                    (dream-cookie-sign secret sid)
+                    {:path "/" :http-only true :same-site "Lax"}))))))))))
+
 ;; ── handler-facing session API ─────────────────────────────────────
 (define dr/session-of (fn (req) (get req :dream-session)))
 (define dream-session-id (fn (req) (get (dr/session-of req) :sid)))

lib/dream/tests/session.sx

@@ -1,4 +1,4 @@
-;; lib/dream/tests/session.sx — cookies, store, session round-trip.
+;; lib/dream/tests/session.sx — cookies, store, session round-trip, signed cookies.
 
 (define dream-ss-pass 0)
 (define dream-ss-fail 0)
@@ -65,6 +65,19 @@
     "Max-Age=0")
   true)
 
+;; ── signed cookie values ───────────────────────────────────────────
+(dream-ss-test
+  "sign/unsign roundtrip"
+  (dream-cookie-unsign "k" (dream-cookie-sign "k" "s5"))
+  "s5")
+(dream-ss-test
+  "unsign wrong secret"
+  (dream-cookie-unsign "k2" (dream-cookie-sign "k" "s5"))
+  nil)
+(dream-ss-test "unsign tampered" (dream-cookie-unsign "k" "s5.999") nil)
+(dream-ss-test "unsign no dot" (dream-cookie-unsign "k" "s5") nil)
+(dream-ss-test "unsign nil" (dream-cookie-unsign "k" nil) nil)
+
 ;; ── in-memory store ────────────────────────────────────────────────
 (define dream-ss-store (dream-memory-sessions))
 (define dream-ss-sid (dream-ss-store {:op "session/create"}))
@@ -93,7 +106,6 @@
         (dream-text (str "count=" (+ n 1)))))))
 (define dream-ss-app ((dream-sessions dream-ss-backend) dream-ss-counter-h))
 
-;; first request: no cookie -> creates session, sets cookie
 (define dream-ss-r1 (dream-ss-app (dream-request "GET" "/" {} "")))
 (dream-ss-test "first body count=1" (dream-resp-body dream-ss-r1) "count=1")
 (dream-ss-test
@@ -109,7 +121,6 @@
   (contains? (first (dream-resp-cookies dream-ss-r1)) "HttpOnly")
   true)
 
-;; second request: carries the cookie -> reuses, sees prior count, no new cookie
 (define dream-ss-r2 (dream-ss-app (dream-request "GET" "/" {:Cookie "dream.session=s1"} "")))
 (dream-ss-test "second body count=2" (dream-resp-body dream-ss-r2) "count=2")
 (dream-ss-test
@@ -117,11 +128,9 @@
   (len (dream-resp-cookies dream-ss-r2))
   0)
 
-;; third request continues
 (define dream-ss-r3 (dream-ss-app (dream-request "GET" "/" {:Cookie "dream.session=s1"} "")))
 (dream-ss-test "third body count=3" (dream-resp-body dream-ss-r3) "count=3")
 
-;; unknown cookie id -> fresh session created
 (define dream-ss-r4 (dream-ss-app (dream-request "GET" "/" {:Cookie "dream.session=bogus"} "")))
 (dream-ss-test
   "bogus id starts fresh"
@@ -133,11 +142,6 @@
   1)
 
 ;; ── session-all + invalidate via middleware ────────────────────────
-(define
-  dream-ss-inspect-h
-  (fn (req) (dream-text (str (dream-session-all req)))))
-(define dream-ss-app2 ((dream-sessions dream-ss-backend) dream-ss-inspect-h))
-(define dream-ss-r5 (dream-ss-app2 (dream-request "GET" "/" {:Cookie "dream.session=s1"} "")))
 (dream-ss-test
   "session-all shows count"
   (dream-session-all
@@ -153,4 +157,41 @@
 (dream-ss-app3 (dream-request "GET" "/" {:Cookie "dream.session=s1"} ""))
 (dream-ss-test "invalidate clears store" (dream-ss-backend {:op "session/exists" :sid "s1"}) false)
 
+;; ── signed session middleware ──────────────────────────────────────
+(define dream-ss-sbackend (dream-memory-sessions))
+(define
+  dream-ss-sapp
+  ((dream-sessions-signed dream-ss-sbackend "topsecret")
+    (fn (req) (dream-text (dream-session-id req)))))
+
+(define dream-ss-sr1 (dream-ss-sapp (dream-request "GET" "/" {} "")))
+(dream-ss-test "signed first sid" (dream-resp-body dream-ss-sr1) "s1")
+(dream-ss-test
+  "signed cookie is signed"
+  (contains? (first (dream-resp-cookies dream-ss-sr1)) "dream.session=s1.")
+  true)
+
+;; forged plaintext sid (no signature) is rejected -> a fresh session is made
+(dream-ss-test
+  "forged plaintext rejected -> new session"
+  (dream-resp-body (dream-ss-sapp (dream-request "GET" "/" {:Cookie "dream.session=s1"} "")))
+  "s2")
+
+;; a validly-signed cookie reuses the session
+(define dream-ss-signed-val (dream-cookie-sign "topsecret" "s1"))
+(define dream-ss-sr3 (dream-ss-sapp (dream-request "GET" "/" {:Cookie (str "dream.session=" dream-ss-signed-val)} "")))
+(dream-ss-test "valid signed reuses s1" (dream-resp-body dream-ss-sr3) "s1")
+(dream-ss-test
+  "valid signed sets no new cookie"
+  (len (dream-resp-cookies dream-ss-sr3))
+  0)
+
+;; a cookie signed with the wrong secret is rejected
+(dream-ss-test
+  "wrong-secret signed rejected"
+  (=
+    (dream-resp-body (dream-ss-sapp (dream-request "GET" "/" {:Cookie (str "dream.session=" (dream-cookie-sign "other" "s1"))} "")))
+    "s1")
+  false)
+
 (define dream-ss-tests-run! (fn () {:total (+ dream-ss-pass dream-ss-fail) :passed dream-ss-pass :failed dream-ss-fail :fails dream-ss-fails}))

plans/dream-on-sx.md

@@ -112,6 +112,13 @@ with extensions + hardening below.
   `dream-json-body` (parse request body). GOTCHA: `number?` is unreliable in this env —
   used `(= (type-of v) "number")`; `parse-float` handles decimals. Multi-key dict
   encode order follows `keys` (non-deterministic) so tests assert via parse round-trip.
+- **2026-06-07 — Ext: signed session cookies** (`lib/dream/session.sx`, session suite
+  30→41, 340 total). The default store uses guessable sids (`s1`, `s2`), so
+  `dream-sessions-signed backend secret` signs the cookie value (`sid.signature`) and
+  rejects any cookie whose signature doesn't verify — a forged plaintext `s1` or a
+  wrong-secret cookie yields a fresh session instead of a hijack. `dream-cookie-sign` /
+  `dream-cookie-unsign` (keyed hash; same not-cryptographic caveat — inject a host HMAC
+  in production). Plain `dream-sessions` unchanged for the no-secret case.
 
 ## Extensions (post-roadmap)
 
@@ -122,7 +129,7 @@ The five-types core is complete; these harden it toward a production HTTP front
 - [x] **Status reason phrases** + `dream-status-text` (`lib/dream/error.sx`).
 - [x] **CORS middleware** (`dream-cors`).
 - [x] **Error-handling middleware** (`dream-catch` / custom 500 templates; `guard`-based).
-- [ ] **Signed session cookies** (the noted hardening — sign the sid).
+- [x] **Signed session cookies** (`dream-sessions-signed` — tamper-evident sid).
 - [x] **JSON helpers** (encode + recursive-descent parse, pure SX).
 - [ ] **Query/header convenience** (`dream-queries`, defaults).
 - [ ] **`api.sx` facade + README** — single load point listing the public surface.