[Question]: Is that a way modify request cookies before it perform?

### Your question

I try to register a handler by page.on("request")
the handler like below:
``` python
def handleRequest(route):
    for key in route.request.headers:
        if key.startswith("cookie"):
            route.request.headers[key] = re.sub(<regex_pattern>, repr, headers[key])
        print(key + ": " + route.request.headers[key]
    route.continue_()
```
but it not work... 