fix: treat already-handled device authorization as success

The /signedin page completes the device authorization flow during a
Server Component render, which the App Router can evaluate more than
once per navigation. The first call authorizes the grant; subsequent
calls fail with FAILED_PRECONDITION ("Device Authorization Request has
already been handled") and surfaced a spurious error even though login
succeeded. Treat that error code as success so the flow is idempotent.

Closes #89

Author: mattdjenkinson

apps/login/src/lib/server/device.ts

@@ -11,10 +11,29 @@ export async function completeDeviceAuthorization(
   const _headers = await headers();
   const { serviceUrl } = getServiceUrlFromHeaders(_headers);
 
-  // without the session, device auth request is denied
-  return authorizeOrDenyDeviceAuthorization({
-    serviceUrl,
-    deviceAuthorizationId,
-    session,
-  });
+  try {
+    // without the session, device auth request is denied
+    return await authorizeOrDenyDeviceAuthorization({
+      serviceUrl,
+      deviceAuthorizationId,
+      session,
+    });
+  } catch (error) {
+    // The /signedin page completes the device flow during a Server Component
+    // render, which the App Router may evaluate more than once per navigation
+    // (RSC refetch, prefetch, refresh, retries). The first call authorizes the
+    // grant successfully; subsequent calls fail with FAILED_PRECONDITION
+    // ("Device Authorization Request has already been handled"). Treat that as
+    // success so the user isn't shown a spurious error after a working login.
+    if (
+      error &&
+      typeof error === "object" &&
+      "code" in error &&
+      error.code === 9 /* FAILED_PRECONDITION */
+    ) {
+      return {};
+    }
+
+    throw error;
+  }
 }