how to disable graphql in Apollo Server?

 It is very convenient to have graphql playground enable on the Apollo Server during the development.

However there will be a security issue if we have this feature enable on the production server. we must 

turn off this feature in the production environment.  we can easily turn on/off this feature on the Apollo

Server configuration setup. I create a environment variable to control this feature.

const apolloServer = new ApolloServer({

        schema: await buildSchema({

          resolvers: [UserResolvers]

        }),

        context: ({ req, res }) => ({ req, res }),

        introspection: process.env.DEV_ENV==="development",

        playground: process.env.DEV_ENV==="development",});