From 8ee844abf69575074cc8db7428db0a46c5808e28 Mon Sep 17 00:00:00 2001
From: Thor Whalen <1906276+thorwhalen@users.noreply.github.com>
Date: Sat, 27 Jun 2026 14:08:01 +0200
Subject: [PATCH] fix(oauth): exempt /auth/oauth/ from platform CSRF
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Claude.ai's dynamic client registration and token exchange are cookieless
machine-to-machine POSTs that can't carry the platform's double-submit CSRF
token — they were 403'ing. /auth/oauth/register + /token are protected by PKCE
+ client validation, and the consent POST carries its own signed token, so the
whole /auth/oauth/ prefix is safe to exempt (gated on oauth_server.enabled).

Claude-Session: https://claude.ai/code/session_0154TnwYASjN1u1Hw97JQ2vd
---
 enlace_auth/plugin.py | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/enlace_auth/plugin.py b/enlace_auth/plugin.py
index ee6d362..3fb5ff4 100644
--- a/enlace_auth/plugin.py
+++ b/enlace_auth/plugin.py
@@ -336,6 +336,12 @@ def wire(parent: "FastAPI", config) -> None:
     # proxy to a black-box upstream that can't participate in enlace's
     # double-submit flow, so their entire mount prefix must also be exempt.
     csrf_exempt = ["/auth/callback", "/auth/login/", "/api/"]
+    if auth_cfg.oauth_server.enabled:
+        # OAuth 2.1 server endpoints: /register + /token are cookieless
+        # machine-to-machine calls (protected by PKCE + client validation), and
+        # the consent POST carries its own signed CSRF token — so the platform's
+        # double-submit CSRF must not gate them.
+        csrf_exempt.append("/auth/oauth/")
     for app in getattr(config, "apps", []):
         if getattr(app, "mode", "asgi") in ("process", "external"):
             prefix = app.route_prefix