Why redirect_uri is required in Authorization flow

[imlonghao]

Hello,

I noticed in RFC 6749 Section 4.1.1, redirect_uri is OPTIONAL.

But in authentik's code, redirect_uri is required.

authentik/authentik/providers/oauth2/views/authorize.py

Lines 191 to 193 in 29b0177

	if not self.redirect_uri:
	LOGGER.warning("Missing redirect uri.")
	raise RedirectUriError("", allowed_redirect_urls).with_cause("redirect_uri_missing")

I think I can hardcode a fixed redirect_uri in authentik, so even the authorize url doesn't have a redirect_uri (e.g. https://<authentik>/application/o/authorize/?client_id=<client_id>&state=<state>&scope=openid&response_type=code), authentik still know where this request should be redirected to.

So may I know why redirect_uri is required in the code?