apollo graphql server privacy control after data is fetched - node.js

Question

So , i don't know how to handle this on a graphql service.
I am migrating a service from rest - express api to an apollo api.
my current mongo schema is like this:
const PostSchema = new mongoose.Schema({
title: { type: String, required: true },
body: { type: String },
uid: { type: mongoose.Schema.Types.ObjectId, ref: 'User', required: true },
privacy: { type: String, enum: ['everyone','followers','onlyme'], default: 'everyone' },
});
const UserSchema = new mongoose.Schema({
name: { type: String, required: true },
followers: [{ type: mongoose.Schema.Types.ObjectId, ref: 'User' }],
});
in express environment i used to get post with populated user the then apply a privacy control function based on user followers.
but in apollo i cant access post after its populated . where can i apply a directive or something after the post fields is resolved?
graphql schema:
type User {
_id: ID!
name: String
followers: [ID]
}
type Post {
_id: ID!
title: String!
body:String
uid :User #privacy
}
extend type Query{
post(_id: String):Post
posts:[Post]
}
post resolver:
{
Query: {
post: (p, a, ctx, info) => {
return ctx.modules.post.getPost(a._id)
}
},
Post: {
uid: (p, a, ctx, info) => {
return ctx.modules.user.getUser(p.uid);
}
},
}