Stuck in a verifying loop on proxy view with Cloudflare's challenge

[ffd000]

I have a view where I pass HTTP auth credentials:

class DjangoProxyView(ProxyView):
    upstream = "https://anothersubdomain"
    def get_request_headers(self):
        headers = super().get_request_headers()
        headers['Authorization'] = f"Basic {creds}"
        return headers

CF requests are being sent to root-domain/<cloudflare endpoint> continuously and failing with a 400.
Everything on the upstream site works correctly.
Is this fixable?