Turn off IIS8 custom errors

Since IIS8, it's not enough to change customErrors=Off to show the error content. There's an extra step to accomplish.

So, here's the changes you  need to make to your web.config to show the errors:

<system.web>
   <customErrors mode="Off" />
</system.web>
<system.webServer>
   <httpErrors existingResponse="PassThrough" errorMode="Detailed">
</system.webServer>