CSP local testing

I need to do some changes to our website, as our CSP prevents Safari from accessing it. Also, the whole security rating of the website is, let's put it nicely, rather bad. Now, is there any way to test changes made to CSP locally, without deploying to the server? I tried ngrok, but that doesn't seem to work (doesn't transmit headers). I'm rather new at this, so any tips would be appreciated!