Improving the performance of a website can be hard. Using solid performance analysis tools is a must.
First, manually access the website by entering your email and then the confirmation code. The next request sets a cookie with the key
That cookie can be set as header when running the performance test. Under Script you are able to define the steps that are taken by WebPageTest during the performance test.
setCookie https://%HOST% CF_Authorization=<value> navigate %URL%