identity: OAuth client registry — public/confidential clients + redirect allow-list (11 tests)

clients.sx (RFC 6749 §2) — confidential clients must present the correct
secret at the token endpoint (wrong → invalid_client); public clients are
identified but not authenticated; redirect_uris are pre-registered and
checked by exact-match valid_redirect (§3.1.2.2 + Security BCP). Standalone
module for now; wiring confidential-client auth into oauth exchange is a
follow-up. New tests/clients.sx. 149/149.

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

lib/identity/clients.sx

@@ -0,0 +1,28 @@
+;; identity/clients.sx — the OAuth client registry (RFC 6749 §2).
+;;
+;; A client is registered with a type, a secret, and its allow-listed
+;; redirect_uris:
+;;
+;;   public        — cannot keep a secret (SPAs, native apps, §2.1);
+;;                   identified but not authenticated.
+;;   confidential  — can authenticate; MUST present its secret at the token
+;;                   endpoint (§3.2.1, §4.1.3). A wrong secret is
+;;                   invalid_client — never a soft pass.
+;;
+;; Redirect URIs must be pre-registered (§3.1.2.2 + OAuth Security BCP):
+;; valid_redirect/3 is the exact-match check the authorize/exchange steps
+;; consult so an attacker cannot redirect the code to an unregistered URI.
+;;
+;;   register(C, ClientId, Type, Secret, RedirectUris) -> ok | {error, exists}
+;;   lookup(C, ClientId)            -> {ok, Type, RedirectUris} | {error, unknown_client}
+;;   authenticate(C, ClientId, Sec) -> {ok, public} | {ok, confidential}
+;;                                   | {error, invalid_client} | {error, unknown_client}
+;;   valid_redirect(C, ClientId, U) -> true | false
+
+(define
+  identity-clients-source
+  "-module(identity_clients).\n\n   start() ->\n     spawn(fun () -> loop([]) end).\n\n   register(C, ClientId, Type, Secret, RedirectUris) ->\n     C ! {register, ClientId, Type, Secret, RedirectUris, self()},\n     receive {client_reply, R} -> R end.\n\n   lookup(C, ClientId) ->\n     C ! {lookup, ClientId, self()},\n     receive {client_reply, R} -> R end.\n\n   authenticate(C, ClientId, Secret) ->\n     C ! {authenticate, ClientId, Secret, self()},\n     receive {client_reply, R} -> R end.\n\n   valid_redirect(C, ClientId, Uri) ->\n     C ! {valid_redirect, ClientId, Uri, self()},\n     receive {client_reply, R} -> R end.\n\n   loop(Clients) ->\n     receive\n       {register, ClientId, Type, Secret, RedirectUris, From} ->\n         case find(ClientId, Clients) of\n           {ok, _} ->\n             From ! {client_reply, {error, exists}},\n             loop(Clients);\n           none ->\n             From ! {client_reply, ok},\n             loop([{ClientId, {Type, Secret, RedirectUris}} | Clients])\n         end;\n       {lookup, ClientId, From} ->\n         case find(ClientId, Clients) of\n           none -> From ! {client_reply, {error, unknown_client}};\n           {ok, {Type, _, Uris}} -> From ! {client_reply, {ok, Type, Uris}}\n         end,\n         loop(Clients);\n       {authenticate, ClientId, Secret, From} ->\n         case find(ClientId, Clients) of\n           none ->\n             From ! {client_reply, {error, unknown_client}};\n           {ok, {public, _, _}} ->\n             From ! {client_reply, {ok, public}};\n           {ok, {confidential, S, _}} ->\n             case S =:= Secret of\n               true -> From ! {client_reply, {ok, confidential}};\n               false -> From ! {client_reply, {error, invalid_client}}\n             end\n         end,\n         loop(Clients);\n       {valid_redirect, ClientId, Uri, From} ->\n         case find(ClientId, Clients) of\n           none -> From ! {client_reply, false};\n           {ok, {_, _, Uris}} -> From ! {client_reply, member(Uri, Uris)}\n         end,\n         loop(Clients);\n       {stop, From} ->\n         From ! {client_reply, ok}\n     end.\n\n   member(_, []) -> false;\n   member(X, [Y | Rest]) ->\n     case X =:= Y of\n       true -> true;\n       false -> member(X, Rest)\n     end.\n\n   find(_, []) -> none;\n   find(Key, [{K, V} | Rest]) ->\n     case K =:= Key of\n       true -> {ok, V};\n       false -> find(Key, Rest)\n     end.")
+
+(define
+  identity-load-clients!
+  (fn () (erlang-load-module identity-clients-source)))

lib/identity/conformance.sh

@@ -39,6 +39,7 @@ SUITES=(
   "audit|id-audit-test-pass|id-audit-test-count"
   "federation|id-fed-test-pass|id-fed-test-count"
   "expiry|id-expiry-test-pass|id-expiry-test-count"
+  "clients|id-clients-test-pass|id-clients-test-count"
 )
 
 cat > "$TMPFILE" << 'EPOCHS'
@@ -59,6 +60,7 @@ cat > "$TMPFILE" << 'EPOCHS'
 (load "lib/identity/cache.sx")
 (load "lib/identity/audit.sx")
 (load "lib/identity/federation.sx")
+(load "lib/identity/clients.sx")
 (load "lib/identity/tests/session.sx")
 (load "lib/identity/tests/token.sx")
 (load "lib/identity/tests/registry.sx")
@@ -70,6 +72,7 @@ cat > "$TMPFILE" << 'EPOCHS'
 (load "lib/identity/tests/audit.sx")
 (load "lib/identity/tests/federation.sx")
 (load "lib/identity/tests/expiry.sx")
+(load "lib/identity/tests/clients.sx")
 (epoch 100)
 (eval "(list id-session-test-pass id-session-test-count)")
 (epoch 101)
@@ -92,6 +95,8 @@ cat > "$TMPFILE" << 'EPOCHS'
 (eval "(list id-fed-test-pass id-fed-test-count)")
 (epoch 110)
 (eval "(list id-expiry-test-pass id-expiry-test-count)")
+(epoch 111)
+(eval "(list id-clients-test-pass id-clients-test-count)")
 EPOCHS
 
 timeout 600 "$SX_SERVER" < "$TMPFILE" > "$OUTFILE" 2>&1

lib/identity/scoreboard.json

@@ -1,7 +1,7 @@
 {
   "language": "identity",
-  "total_pass": 138,
-  "total": 138,
+  "total_pass": 149,
+  "total": 149,
   "suites": [
     {"name":"session","pass":11,"total":11,"status":"ok"},
     {"name":"token","pass":24,"total":24,"status":"ok"},
@@ -13,6 +13,7 @@
     {"name":"cache","pass":9,"total":9,"status":"ok"},
     {"name":"audit","pass":11,"total":11,"status":"ok"},
     {"name":"federation","pass":12,"total":12,"status":"ok"},
-    {"name":"expiry","pass":8,"total":8,"status":"ok"}
+    {"name":"expiry","pass":8,"total":8,"status":"ok"},
+    {"name":"clients","pass":11,"total":11,"status":"ok"}
   ]
 }

lib/identity/scoreboard.md

@@ -1,6 +1,6 @@
 # identity-on-sx Scoreboard
 
-**Total: 138 / 138 tests passing**
+**Total: 149 / 149 tests passing**
 
 |  | Suite | Pass | Total |
 |---|---|---|---|
@@ -15,6 +15,7 @@
 | ✅ | audit | 11 | 11 |
 | ✅ | federation | 12 | 12 |
 | ✅ | expiry | 8 | 8 |
+| ✅ | clients | 11 | 11 |
 
 
 Generated by `lib/identity/conformance.sh`.

lib/identity/tests/clients.sx

@@ -0,0 +1,108 @@
+;; identity/tests/clients.sx — OAuth client registry: registration,
+;; public vs confidential authentication, and redirect_uri allow-listing.
+
+(define id-clients-test-count 0)
+(define id-clients-test-pass 0)
+(define id-clients-test-fails (list))
+
+(define
+  id-clients-test
+  (fn
+    (name actual expected)
+    (set! id-clients-test-count (+ id-clients-test-count 1))
+    (if
+      (= actual expected)
+      (set! id-clients-test-pass (+ id-clients-test-pass 1))
+      (append! id-clients-test-fails {:name name :expected expected :actual actual}))))
+
+(define idc-ev erlang-eval-ast)
+(define idcnm (fn (v) (get v :name)))
+
+(identity-load-clients!)
+
+;; ── registration + lookup ────────────────────────────────────────
+
+(id-clients-test
+  "a registered client looks up its type"
+  (idcnm
+    (idc-ev
+      "C = identity_clients:start(),\n       identity_clients:register(C, app1, confidential, s3cret, [uri1]),\n       case identity_clients:lookup(C, app1) of\n         {ok, Type, _} -> Type;\n         {error, W} -> W\n       end"))
+  "confidential")
+
+(id-clients-test
+  "registering the same client twice is an error"
+  (idcnm
+    (idc-ev
+      "C = identity_clients:start(),\n       identity_clients:register(C, app1, confidential, s3cret, [uri1]),\n       case identity_clients:register(C, app1, public, none, [uri1]) of\n         ok -> ok;\n         {error, W} -> W\n       end"))
+  "exists")
+
+(id-clients-test
+  "looking up an unregistered client is unknown_client"
+  (idcnm
+    (idc-ev
+      "C = identity_clients:start(),\n       case identity_clients:lookup(C, ghost) of\n         {ok, _, _} -> found;\n         {error, W} -> W\n       end"))
+  "unknown_client")
+
+;; ── confidential client authentication ───────────────────────────
+
+(id-clients-test
+  "a confidential client authenticates with the right secret"
+  (idcnm
+    (idc-ev
+      "C = identity_clients:start(),\n       identity_clients:register(C, app1, confidential, s3cret, [uri1]),\n       case identity_clients:authenticate(C, app1, s3cret) of\n         {ok, Kind} -> Kind;\n         {error, W} -> W\n       end"))
+  "confidential")
+
+(id-clients-test
+  "a confidential client with the wrong secret is invalid_client"
+  (idcnm
+    (idc-ev
+      "C = identity_clients:start(),\n       identity_clients:register(C, app1, confidential, s3cret, [uri1]),\n       case identity_clients:authenticate(C, app1, wrongsecret) of\n         {ok, _} -> accepted;\n         {error, W} -> W\n       end"))
+  "invalid_client")
+
+(id-clients-test
+  "a public client needs no secret to authenticate"
+  (idcnm
+    (idc-ev
+      "C = identity_clients:start(),\n       identity_clients:register(C, spa, public, none, [uri1]),\n       case identity_clients:authenticate(C, spa, anything) of\n         {ok, Kind} -> Kind;\n         {error, W} -> W\n       end"))
+  "public")
+
+(id-clients-test
+  "authenticating an unknown client is unknown_client"
+  (idcnm
+    (idc-ev
+      "C = identity_clients:start(),\n       case identity_clients:authenticate(C, ghost, x) of\n         {ok, _} -> accepted;\n         {error, W} -> W\n       end"))
+  "unknown_client")
+
+;; ── redirect_uri allow-listing ───────────────────────────────────
+
+(id-clients-test
+  "a registered redirect_uri is valid"
+  (idcnm
+    (idc-ev
+      "C = identity_clients:start(),\n       identity_clients:register(C, app1, confidential, s3cret, [uri1, uri2]),\n       case identity_clients:valid_redirect(C, app1, uri1) of\n         true -> yes;\n         false -> no\n       end"))
+  "yes")
+
+(id-clients-test
+  "a second registered redirect_uri is also valid"
+  (idcnm
+    (idc-ev
+      "C = identity_clients:start(),\n       identity_clients:register(C, app1, confidential, s3cret, [uri1, uri2]),\n       case identity_clients:valid_redirect(C, app1, uri2) of\n         true -> yes;\n         false -> no\n       end"))
+  "yes")
+
+(id-clients-test
+  "an unregistered redirect_uri is rejected"
+  (idcnm
+    (idc-ev
+      "C = identity_clients:start(),\n       identity_clients:register(C, app1, confidential, s3cret, [uri1]),\n       case identity_clients:valid_redirect(C, app1, evil_uri) of\n         true -> yes;\n         false -> no\n       end"))
+  "no")
+
+(id-clients-test
+  "redirect validation for an unknown client is rejected"
+  (idcnm
+    (idc-ev
+      "C = identity_clients:start(),\n       case identity_clients:valid_redirect(C, ghost, uri1) of\n         true -> yes;\n         false -> no\n       end"))
+  "no")
+
+(define
+  id-clients-test-summary
+  (str "clients " id-clients-test-pass "/" id-clients-test-count))

plans/identity-on-sx.md

@@ -19,7 +19,7 @@ through the event log, all authorization questions delegated to `acl-on-sx`.
 
 ## Status (rolling)
 
-`bash lib/identity/conformance.sh` → **138/138** (4 phases + ext: scope narrowing, token TTL)
+`bash lib/identity/conformance.sh` → **149/149** (4 phases + ext: scope, TTL, client registry)
 
 ## Ground rules
 
@@ -81,13 +81,19 @@ lib/identity/api.sx ── (identity/login) (identity/grant?) (identity/revoke)
 - [~] PKCE S256 method (RFC 7636 §4.2) — BLOCKED on erlang substrate (see Blockers)
 - [x] access-token TTL / `expires_in` — logical-clock expiry, introspect honours it
 - [x] scope as a set + scope narrowing on refresh (RFC 6749 §6)
-- [ ] client registry: public vs confidential clients, client authentication (RFC 6749 §2)
+- [x] client registry: public vs confidential clients, client authentication (RFC 6749 §2)
 - [ ] client-credentials grant (RFC 6749 §4.4) and device grant (RFC 8628)
 - [ ] acl-on-sx delegation: wire `verify`/membership projection → an acl decision, integration test
 - [ ] OAuth `state` (CSRF) + OIDC `nonce` threaded through authorize→exchange
 - [ ] unify `api.sx` over oauth + membership + audit (one facade, audited login/consent)
 
 ## Progress log
+- 2026-06-07 — `clients.sx` (ext): OAuth client registry (RFC 6749 §2). public
+  vs confidential clients; confidential clients MUST present the right secret
+  (wrong → invalid_client), public clients are identified but not
+  authenticated; redirect_uris are allow-listed with exact-match
+  `valid_redirect` (§3.1.2.2 + Security BCP). Standalone module (no oauth
+  wiring yet — that's a follow-up). New tests/clients.sx (11). 138→149.
 - 2026-06-07 — access-token expiry (ext): logical clock in the token registry
   (`advance`/`now`; no wall clock in substrate). Grants carry a Ttl; each
   access token carries an Expires (Now-at-issue + Ttl, or infinity); introspect