webpack.config.js

// ...

// Near the bottom of the file, before the `module.exports`,
// paste in the following code:
const requestProcessor = Object.assign(
    {},
    {
        entry: './app/request-processor.js',
        target: 'node',
        output: {
            path: path.resolve(process.cwd(), 'build'),
            filename: 'request-processor.js',
            // Output a CommonJS module for use in Node
            libraryTarget: 'commonjs2'
        },
        module: {
            rules: [
                {
                    test: /\.js$/,
                    exclude: /node_modules/,
                    use: {
                        loader: 'babel-loader',
                        options: {
                            cacheDirectory: path.join(__dirname, 'tmp')
                        }
                    }
                }
            ]
        }
    }
)

// Modify the module.export to include the new `requestProcessor` object
module.exports = [main, others, ssrServerConfig, requestProcessor]