Netlify Identity Widget is being loaded on all pages in production

Description

Netlify Identity Widget is being loaded on the index page in production. This makes user to load unnecessary 50kb of js.

Steps to reproduce

1. Add gatsby-plugin-netlify-cms to gatsby project
2. npm run build
3. npm run serve
4. Check network tab

Expected result

Netlify Identity Widget should be loaded only on the /admin page

Actual result

Netlify Identity Widget is being loaded on all pages in production

Environment

System: OS: macOS Mojave 10.14 CPU: (4) x64 Intel® Core™ i7-5557U CPU @ 3.10GHz Shell: 5.3 - /bin/zsh Binaries: Node: 11.15.0 - /usr/local/bin/node Yarn: 1.21.1 - /usr/local/bin/yarn npm: 6.7.0 - /usr/local/bin/npm Languages: Python: 2.7.10 - /usr/bin/python Browsers: Chrome: 79.0.3945.130 Firefox: 72.0.1 Safari: 12.0 npmPackages: gatsby: 2.19.10 => 2.19.10 gatsby-image: 2.2.39 => 2.2.39 gatsby-plugin-netlify: 2.1.31 => 2.1.31 gatsby-plugin-netlify-cms: 4.1.37 => 4.1.37 gatsby-plugin-netlify-cms-paths: 1.3.0 => 1.3.0 gatsby-plugin-postcss: 2.1.19 => 2.1.19 gatsby-plugin-preact: 3.1.25 => 3.1.25 gatsby-plugin-react-helmet: 3.1.21 => 3.1.21 gatsby-plugin-sharp: 2.4.4 => 2.4.4 gatsby-plugin-svgr: 2.0.2 => 2.0.2 gatsby-plugin-typescript: 2.1.26 => 2.1.26 gatsby-plugin-webpack-bundle-analyzer: 1.0.5 => 1.0.5 gatsby-source-filesystem: 2.1.47 => 2.1.47 gatsby-source-hubspot: 2.0.3 => 2.0.3 gatsby-transformer-sharp: 2.3.13 => 2.3.13 gatsby-transformer-yaml: 2.2.23 => 2.2.23 npmGlobalPackages: gatsby-cli: 2.7.34

[smashercosmo]

Maybe worth adding this advice to the docs

[abdullahe]

This section was recently added to the readme: https://github.com/gatsbyjs/gatsby/tree/master/packages/gatsby-plugin-netlify-cms#disable-widget-on-site

Hi. I don’t know if it is better to open a new issue but trying what @erezrokah suggested above. When I try this, I see a blank page at /admin.

Here is the gatsby-config.js part:

{
      resolve: `gatsby-plugin-netlify-cms`,
      options: {
        modulePath: `${__dirname}/src/cms/cms.js`,
        enableIdentityWidget: true,
        includeRobots: false,
        publicPath: `admin`,
      },
 },

And here is the gatsby-node.js part:

const webpack = require(`webpack`);

exports.onCreateWebpackConfig = ({ actions }) => {
  actions.setWebpackConfig({
    plugins: [
      new webpack.IgnorePlugin({
        resourceRegExp: /^netlify-identity-widget$/,
      }),
    ],
  });
};