How add paths to sass include path?

How can custom/external paths be added to include paths used by sass in latest sage (9.x)?
I sifted through the webpack config and scripts but I can’t find the place that is responsible for compiling with sass.

I was able to configure the includePath in webpack.config.js:

`sass?${sourceMapQueryStr}&includePaths[]=/share/scss/`,

Options are passed to plugins like parameters in URLs.

Alternatively an object can be passed instead the string sass?${sourceMapQueryStr},:

    [...],
    `resolve-url?${sourceMapQueryStr}`,
    {
      loader: `sass?${sourceMapQueryStr}`,
      options: {
          includePaths: ['/share/scss/']
      }
    }

If anyone is interested in using eyeglass with sass-loader in webpack,
here the adjusted code/config for integrating it - example for extra include paths included:

[...]
{
    test: /\.scss$/,
    include: config.paths.assets,
    use: ExtractTextPlugin.extract({
      fallback: 'style',
      publicPath: '../',
      use: [
        `css?${sourceMapQueryStr}`,
        'postcss',
        `resolve-url?${sourceMapQueryStr}`,
        {
          loader: `sass?${sourceMapQueryStr}`,
          options: eyeglass({
              // sass options...
              includePaths: ['/share/scss/'],
              eyeglass: {
                // eyeglass options
              }
            })
        }
      ],
    }),
 },
 [...]