identity: refresh-token rotation + cascading revocation (token.sx grant-centric, +9 tests)

The grant {Subject,Client,Scope,Status} becomes the unit of authorization
and cascade; access + refresh tokens reference it. issue_grant returns an
access+refresh pair; refresh (RFC 6749 §6) supersedes the presented refresh
token and mints a fresh pair; reusing a superseded refresh token is treated
as theft (RFC 6819 §5.2.2.3) and revokes the whole family, killing the live
descendant. revoke of any token cascades to the grant. All prior token
behaviour preserved. token 18/18, 62/62.

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

lib/identity/tests/token.sx

@@ -1,6 +1,7 @@
-;; identity/tests/token.sx — opaque tokens, grant-backed lookup, and
-;; real revocation. The revoke-then-introspect path is the security
-;; centrepiece: a revoked token must read inactive immediately.
+;; identity/tests/token.sx — opaque tokens, grant-backed lookup, real
+;; revocation, refresh-token rotation, and cascading revocation. The
+;; revoke-then-introspect and refresh-reuse paths are the security
+;; centrepieces.
 
 (define id-token-test-count 0)
 (define id-token-test-pass 0)
@@ -94,6 +95,77 @@
       "Reg = identity_tokens:start(),\n       {ok, A} = identity_tokens:issue(Reg, alice, web, read),\n       {ok, B} = identity_tokens:issue(Reg, alice, cli, read),\n       identity_tokens:revoke(Reg, A),\n       case identity_tokens:introspect(Reg, B) of\n         {active, _, _, _} -> active;\n         {inactive} -> inactive\n       end"))
   "active")
 
+;; ── issue_grant: access + refresh pair (RFC 6749 §4.1.4 / §5.1) ───
+
+(id-token-test
+  "issue_grant access token introspects active"
+  (idtnm
+    (idt-ev
+      "Reg = identity_tokens:start(),\n       {ok, A, _R} = identity_tokens:issue_grant(Reg, alice, web, read),\n       case identity_tokens:introspect(Reg, A) of\n         {active, _, _, _} -> active;\n         {inactive} -> inactive\n       end"))
+  "active")
+
+;; ── refresh rotation (RFC 6749 §6) ───────────────────────────────
+
+(id-token-test
+  "refresh mints a working new access token"
+  (idtnm
+    (idt-ev
+      "Reg = identity_tokens:start(),\n       {ok, _A, R} = identity_tokens:issue_grant(Reg, alice, web, read),\n       {ok, A2, _R2} = identity_tokens:refresh(Reg, R),\n       case identity_tokens:introspect(Reg, A2) of\n         {active, _, _, _} -> active;\n         {inactive} -> inactive\n       end"))
+  "active")
+
+(id-token-test
+  "rotated token keeps the grant's subject"
+  (idtnm
+    (idt-ev
+      "Reg = identity_tokens:start(),\n       {ok, _A, R} = identity_tokens:issue_grant(Reg, alice, web, read),\n       {ok, A2, _R2} = identity_tokens:refresh(Reg, R),\n       case identity_tokens:introspect(Reg, A2) of\n         {active, Subject, _, _} -> Subject\n       end"))
+  "alice")
+
+(id-token-test
+  "refresh chains across rotations"
+  (idtnm
+    (idt-ev
+      "Reg = identity_tokens:start(),\n       {ok, _A, R} = identity_tokens:issue_grant(Reg, alice, web, read),\n       {ok, _A2, R2} = identity_tokens:refresh(Reg, R),\n       {ok, A3, _R3} = identity_tokens:refresh(Reg, R2),\n       case identity_tokens:introspect(Reg, A3) of\n         {active, _, _, _} -> active;\n         {inactive} -> inactive\n       end"))
+  "active")
+
+(id-token-test
+  "refreshing an unknown token is invalid_grant"
+  (idtnm
+    (idt-ev
+      "Reg = identity_tokens:start(),\n       Bogus = make_ref(),\n       case identity_tokens:refresh(Reg, Bogus) of\n         {ok, _, _} -> rotated;\n         {error, Why} -> Why\n       end"))
+  "invalid_grant")
+
+;; ── refresh-token reuse = theft → revoke the family (RFC 6819) ────
+
+(id-token-test
+  "reusing a superseded refresh token is invalid_grant"
+  (idtnm
+    (idt-ev
+      "Reg = identity_tokens:start(),\n       {ok, _A, R} = identity_tokens:issue_grant(Reg, alice, web, read),\n       {ok, _A2, _R2} = identity_tokens:refresh(Reg, R),\n       case identity_tokens:refresh(Reg, R) of\n         {ok, _, _} -> rotated;\n         {error, Why} -> Why\n       end"))
+  "invalid_grant")
+
+(id-token-test
+  "refresh reuse revokes the live descendant too"
+  (idtnm
+    (idt-ev
+      "Reg = identity_tokens:start(),\n       {ok, _A, R} = identity_tokens:issue_grant(Reg, alice, web, read),\n       {ok, A2, _R2} = identity_tokens:refresh(Reg, R),\n       identity_tokens:refresh(Reg, R),\n       case identity_tokens:introspect(Reg, A2) of\n         {active, _, _, _} -> still_valid;\n         {inactive} -> inactive\n       end"))
+  "inactive")
+
+;; ── cascading revocation: revoke any token, the grant dies ───────
+
+(id-token-test
+  "revoking the access token blocks refresh"
+  (idtnm
+    (idt-ev
+      "Reg = identity_tokens:start(),\n       {ok, A, R} = identity_tokens:issue_grant(Reg, alice, web, read),\n       identity_tokens:revoke(Reg, A),\n       case identity_tokens:refresh(Reg, R) of\n         {ok, _, _} -> refreshed;\n         {error, Why} -> Why\n       end"))
+  "invalid_grant")
+
+(id-token-test
+  "revoking the refresh token deactivates the access token"
+  (idtnm
+    (idt-ev
+      "Reg = identity_tokens:start(),\n       {ok, A, R} = identity_tokens:issue_grant(Reg, alice, web, read),\n       identity_tokens:revoke(Reg, R),\n       case identity_tokens:introspect(Reg, A) of\n         {active, _, _, _} -> active;\n         {inactive} -> inactive\n       end"))
+  "inactive")
+
 (define
   id-token-test-summary
   (str "token " id-token-test-pass "/" id-token-test-count))