How to use webpack proxy devserver pathRewrite?

I'm currently struggling with rewriting the proxy path to the api server. In my setup what I do is for api request, I delegate it to the proxy server and only for js/html/css webpack-dev-server is used.

Following is what I'm using:

devServer: {
    inline: true,
    port: 8080,
    historyApiFallback: true,
    publicPath: 'http://localhost:8080/dist/',
    disableHostCheck: true,
    proxy: {
        '/api': {
        target: 'http://localhost:3000',
        pathRewrite: {'???' : ''} //Need to append http://localhost:3000/MySite1/api
  }
}

So, How do I append /MySite1 to api request before it proxies to the localhost:3000?

E.g. If the request is : http://localhost:8080/api, it should re write to http://localhost:3000/MySite1/api

Also, If the request is : http://localhost:8080, it should re write to http://localhost:3000/MySite1

Try following:

devServer: {
inline: true,
port: 8080,
historyApiFallback: true,
publicPath: 'http://localhost:8080/dist/',
disableHostCheck: true,
proxy: {
     '/api': {
     target: 'http://localhost:3000',
      pathRewrite: function(path, req) {
       var replacedPath = path;
       if (path.indexOf("MySite1") === -1) {
         replacedPath = replacedPath.replace("/", "/MySite1/api/");
       }
       return replacedPath;
     },
  }
}