replace 3pid option

Adds the option to replace 3pid from the external datasource in synapse. In this case, all 3pids that are not listed in the external store are deleted from synapse on login.

rest_auth_provider.py

@@ -90,9 +90,12 @@ class RestAuthProvider(object):
             if (self.config.updateThreepid):
                 if "three_pids" in profile:
                     logger.info("Handling 3PIDs")
+
+                    external_3pids = []
                     for threepid in profile["three_pids"]:
                         medium = threepid["medium"].lower()
                         address = threepid["address"].lower()
+                        external_3pids.append({"medium": medium, "address": address})
                         logger.info("Looking for 3PID %s:%s in user profile", medium, address)
 
                         validated_at = self.account_handler.hs.get_clock().time_msec()
@@ -107,6 +110,20 @@ class RestAuthProvider(object):
                             )
                         else:
                             logger.info("3PID is present, skipping")
+
+                    if (self.config.replaceThreepid):
+                        for threepid in (yield store.user_get_threepids(user_id)):
+                            medium = threepid["medium"].lower()
+                            address = threepid["address"].lower()
+                            if {"medium": medium, "address": address} not in external_3pids:
+                                logger.info("3PID is not present in external datastore, deleting")
+                                yield store.user_delete_threepid(
+                                    user_id,
+                                    medium,
+                                    address
+                                )
+
+
             else:
                 logger.info("3PIDs were not updated due to policy")
         else:
@@ -125,6 +142,7 @@ class RestAuthProvider(object):
             setNameOnRegister = True
             setNameOnLogin = False
             updateThreepid = True
+            replaceThreepid = False
 
         rest_config = _RestConfig()
         rest_config.endpoint = config["endpoint"]
@@ -165,6 +183,15 @@ class RestAuthProvider(object):
             # we don't care
             pass
 
+        try:
+            rest_config.replaceThreepid = config['policy']['all']['threepid']['replace']
+        except TypeError:
+            # we don't care
+            pass
+        except KeyError:
+            # we don't care
+            pass
+
         return rest_config
 
 def _require_keys(config, required):
@@ -175,4 +202,3 @@ def _require_keys(config, required):
                 ", ".join(missing)
             )
         )
-