feat: Add trust proxy configuration support

Introduces a 'trust_proxy' setting in the configuration file to
handle client IP addresses correctly. Updates logic in the
EmailInputView to extract the client IP based on trust proxy
settings, improving flexibility for deployments behind proxies.

Relates to handling requests within various network environments.

config.dist.yaml

@@ -12,3 +12,4 @@ email:
   tls: true
 admin:
   email: admin@your.server
+trust_proxy: false

src/synapse_registration/registration/views.py

@@ -52,11 +52,17 @@ class EmailInputView(FormView):
             return self.form_invalid(form)
 
         token = token_urlsafe(32)
+
+        if not settings.TRUST_PROXY:
+            ip_address = self.request.META.get("REMOTE_ADDR")
+        else:
+            ip_address = self.request.META.get("HTTP_X_FORWARDED_FOR")
+
         UserRegistration.objects.create(
             username=self.request.session["username"],
             email=email,
             token=token,
-            ip_address=self.request.META.get("REMOTE_ADDR"),
+            ip_address=ip_address,
         )
         verification_link = self.request.build_absolute_uri(
             reverse_lazy("verify_email", args=[token])

src/synapse_registration/synapse_registration/settings.py

@@ -47,6 +47,8 @@ DEBUG = config.get("debug", False)
 
 ALLOWED_HOSTS = config.get("hosts")
 
+TRUST_PROXY = config.get("trust_proxy", False)
+
 if not ALLOWED_HOSTS:
     raise KeyError("Please specify a list of allowed hosts in the configuration file.")