[mod] limiter: trusted proxies (#4911)

Replaces `x_for` functionality with `trusted_proxies`. This allows defining
which IP / ranges to trust extracting the client IP address from X-Forwarded-For
and X-Real-IP headers.

We don't know if the proxy chain will give us the proper client
address (REMOTE_ADDR in the WSGI environment), so we rely on reading the headers
of the proxy before SearXNG (if there is one, in that case it must be added to
trusted_proxies) hoping it has done the proper checks. In case a proxy in the
chain does not check the client address correctly, integrity is compromised and
this should be fixed by whoever manages the proxy, not us.

Closes:

- https://github.com/searxng/searxng/issues/4940
- https://github.com/searxng/searxng/issues/4939
- https://github.com/searxng/searxng/issues/4907
- https://github.com/searxng/searxng/issues/3632
- https://github.com/searxng/searxng/issues/3191
- https://github.com/searxng/searxng/issues/1237

Related:

- https://github.com/searxng/searxng-docker/issues/386
- https://github.com/inetol-infrastructure/searxng-container/issues/81

searx/plugins/tor_check.py

@@ -5,6 +5,7 @@ user searches for ``tor-check``.  It fetches the tor exit node list from
 user's IP address is in it.
 """
 from __future__ import annotations
+from ipaddress import ip_address
 import typing
 
 import re
@@ -14,7 +15,6 @@ from httpx import HTTPError
 from searx.network import get
 from searx.plugins import Plugin, PluginInfo
 from searx.result_types import EngineResults
-from searx.botdetection import get_real_ip
 
 if typing.TYPE_CHECKING:
     from searx.search import SearchWithPlugins
@@ -66,7 +66,7 @@ class SXNGPlugin(Plugin):
                 results.add(results.types.Answer(answer=f"{msg} {url_exit_list}"))
                 return results
 
-            real_ip = get_real_ip(request)
+            real_ip = ip_address(address=str(request.remote_addr)).compressed
 
             if real_ip in node_list:
                 msg = gettext("You are using Tor and it looks like you have the external IP address")