bool.cx

If you trying to setup Strapi CMS and you see this issue with previews

You just need to configure security plugin in the middleware

  {
    name: 'strapi::security',
    config: {
      contentSecurityPolicy: {
        useDefaults: true,
        directives: {
          'connect-src': [
            "'self'", 
            'https:'
          ],
          'img-src': [
            "'self'",
            'data:',
            'blob:',
            'storage.googleapis.com',
            'market-assets.strapi.io'
          ],
          'media-src': [
            "'self'", 
            'data:', 
            'blob:', 
            'storage.googleapis.com',            
          ],
          upgradeInsecureRequests: null,
        },
      }
    }
  },

https://helmetjs.github.io/

https://docs.strapi.io/cms/configurations/middlewares#security