如何从graphql突变中返回令牌

type Mutation {
  generateToken(username: String!, password: String!): Token!
}

type Token {
  accessToken: String!
  refreshToken: String!
}

const { GraphQLObjectType, GraphQLString, GraphQLNonNull } = require('graphql');

const MutationType = new GraphQLObjectType({
  name: 'Mutation',
  fields: {
    generateToken: {
      type: TokenType,
      args: {
        username: { type: new GraphQLNonNull(GraphQLString) },
        password: { type: new GraphQLNonNull(GraphQLString) },
      },
      resolve: async (_, { username, password }) => {
        // 验证用户身份和凭据
        const isValidCredentials = await authenticateUser(username, password);
        if (!isValidCredentials) {
          throw new Error('Invalid credentials');
        }

        // 生成令牌
        const accessToken = generateAccessToken(username);
        const refreshToken = generateRefreshToken(username);

        // 保存令牌到数据库或其他存储
        await saveTokenToDatabase(username, accessToken, refreshToken);

        // 返回令牌
        return { accessToken, refreshToken };
      },
    },
  },
});

const TokenType = new GraphQLObjectType({
  name: 'Token',
  fields: {
    accessToken: { type: GraphQLString },
    refreshToken: { type: GraphQLString },
  },
});