middleware rxjs support

src/registry/registries/do-register.ts

@@ -107,7 +107,14 @@ export namespace DoRegister {
   export const middleware = registry.define(
     'middleware',
     (prepend, ctx, obj, key) =>
-      ctx.middleware((session, next) => obj[key](session, next), prepend),
+      ctx.middleware(async (session, next) => {
+        const ret = await obj[key](session, next);
+        if (isObservable(ret)) {
+          return sessionRxToPromise(session, ret as Observable<string>);
+        } else {
+          return ret;
+        }
+      }, prepend),
   );
 
   export const event = registry.define('onEvent', (data, ctx, obj, key) =>