Strapi Restrict User to Retrieve data only related to him (Strapi V4.0)

src\policies\restrict-user.js

/**
 * Strapi Restrict User to Retrieve data only related to him (Strapi V4.0)
 * 
 * @author Masoud Zohrabi <[email protected]>
 */

module.exports = (ctx, config, {strapi}) => {
    // Assert user logged-in
    if (!ctx.state.user) return false;

    // Rest API
    if (ctx.request) {

        // Check user query
        if (ctx.request.query?.user && ctx.request.query?.user == ctx.state.user.id)
            return true;

        // Set user filter
        if (!ctx.request.query.user) {
            ctx.request.query.user = ctx.state.user.id;
            return true;
        }

    // GraphQL
    } else if (ctx.info) {
        ctx.args.filters = ctx.args.filters || {};
        ctx.args.filters.user = { id: { eq: ctx.state.user.id } };
        return true;
    }

    // Deny access
    return false;
}

Usage Example

Register GraphQL Policy

// src/index.js

'use strict';

module.exports = {
  /**
   * An asynchronous register function that runs before
   * your application is initialized.
   *
   * This gives you an opportunity to extend code.
   */
  register({ strapi }) {
    // GraphQL Policy
    const extensionService = strapi.plugin('graphql').service('extension');
    extensionService.use({
      resolversConfig: {
        'Query.posts': {
          policies: [
            'global::restrict-user'
          ]
        }
      }
    })

  },

  /**
   * An asynchronous bootstrap function that runs before
   * your application gets started.
   *
   * This gives you an opportunity to set up your data model,
   * run jobs, or perform some special logic.
   */
  bootstrap(/*{ strapi }*/) {},
};

Apply Policy on Controller (REST)

// src/api/post/routes/post.js

'use strict';

/**
 * post router.
 */

const { createCoreRouter } = require('@strapi/strapi').factories;

module.exports = createCoreRouter('api::post.post', {   
    config: {
        find: {
            policies: ['global::restrict-user']
        }
    }
});