Graphql shield returns Not Authorised for allowed mutation

I am trying to implement GraphQL API using apollo-server-express. I want to manage permissions by graphql-shield middleware but I am having issues with allowing execution of mutations. My goal is to have JWT based authentication but to allow execution of some queries/mutations to unauthenticated users which is needed for register/login mutations. There for I am using default allow rule. But when I try to run login mutation, I receive Not Authorised! error. I have no clue why is that. The rule works fine with queries.

Thank you for the answer.

Server

import express from "express";
import cors from "cors";
import { ApolloServer, makeExecutableSchema } from "apollo-server-express";
import config from "./config";
import mockResolver from "./resolvers/mockResolver";
import typeDefs from "./graphql/typeDefs";
import { applyMiddleware } from "graphql-middleware";
import permissions from "./graphql/permissions";

const app = express();
app.use(cors());

const server = new ApolloServer({
  schema: applyMiddleware(
    makeExecutableSchema({ typeDefs, resolvers: mockResolver }),
    permissions
  ),
  playground: true,
  introspection: true,
});

server.applyMiddleware({ app, path: "/graphql" });
app.listen(config.PORT, () =>
  console.log("Server listening at http://localhost:%s", config.PORT)
);

TypeDefs

import { gql } from "apollo-server";

const typeDefs = gql`
  type User {
    id: Int!
    email: String!
    password: String!
  }

  type LoginResponse {
    id: String
    email: String
    token: String
  }

  type Query {
    user(id: Int!): User
    users: [User]
  }

  type Mutation {
    login(email: String!, password: String!): LoginResponse
  }
`;

Permissions

import { shield, allow } from "graphql-shield";

const permissions = shield({
  Query: {
    users: allow,
  },
  Mutation: {
    login: allow,
  },
});

export default permissions;