auth: dovecot: pass remote IP (rip=) to auth server

If known, let the auth server know where the client came
from, using REMOTE_ADDR or, optionally/configurably, the
X-Remote-Addr header value (which is needed when running
behind a trusted proxy.)

Addresses #1859.

radicale/config.py

@@ -253,6 +253,10 @@ DEFAULT_CONFIG_SCHEMA: types.CONFIG_SCHEMA = OrderedDict([
             "value": "12345",
             "help": "dovecot auth port",
             "type": int}),
+        ("dovecot_rip_x_remote_addr", {
+            "value": "False",
+            "help": "use X-Remote-Addr for dovecot auth remote IP (rip) parameter",
+            "type": bool}),
         ("realm", {
             "value": "Radicale - Password Required",
             "help": "message displayed when a password is needed",