diff --git a/src/lib/http/middleware/authenticate.ts b/src/lib/http/middleware/authenticate.ts
index da21f707..19fcd267 100644
--- a/src/lib/http/middleware/authenticate.ts
+++ b/src/lib/http/middleware/authenticate.ts
@@ -26,3 +26,5 @@ export const authenticate: ExtendedMiddleware = async (ctx, next) => {
 
 	return next();
 };
+
+export type AuthenticateState = { userId?: string };
diff --git a/src/types.d.ts b/src/types.d.ts
index 0a804c86..c53b4b7d 100644
--- a/src/types.d.ts
+++ b/src/types.d.ts
@@ -1,8 +1,9 @@
 import type Koa from 'koa';
 import type Router from '@koa/router';
 import type { DocsLinkContext } from './lib/http/middleware/docs-link.js';
+import type { AuthenticateState } from './lib/http/middleware/authenticate.js';
 
-export type CustomState = Koa.DefaultState & { userId?: string };
+export type CustomState = Koa.DefaultState & AuthenticateState;
 export type CustomContext = Koa.DefaultContext & DocsLinkContext;
 
 export type ExtendedContext = Router.RouterContext<CustomState, CustomContext>;