Add ability to perform password reset via email without trusting the identity server (#5377)

Sends password reset emails from the homeserver instead of proxying to the identity server. This is now the default behaviour for security reasons. If you wish to continue proxying password reset requests to the identity server you must now enable the email.trust_identity_server_for_password_resets option.

This PR is a culmination of 3 smaller PRs which have each been separately reviewed:

* #5308
* #5345
* #5368

2 files changed, 69 insertions, 20 deletions

diff --git a/synapse/push/mailer.py b/synapse/push/mailer.py
index c269bcf4a4..4bc9eb7313 100644
--- a/synapse/push/mailer.py
+++ b/synapse/push/mailer.py
@@ -80,10 +80,10 @@ ALLOWED_ATTRS = {
 
 
 class Mailer(object):
-    def __init__(self, hs, app_name, notif_template_html, notif_template_text):
+    def __init__(self, hs, app_name, template_html, template_text):
         self.hs = hs
-        self.notif_template_html = notif_template_html
-        self.notif_template_text = notif_template_text
+        self.template_html = template_html
+        self.template_text = template_text
 
         self.sendmail = self.hs.get_sendmail()
         self.store = self.hs.get_datastore()
@@ -94,21 +94,48 @@ class Mailer(object):
         logger.info("Created Mailer for app_name %s" % app_name)
 
     @defer.inlineCallbacks
-    def send_notification_mail(self, app_id, user_id, email_address,
-                               push_actions, reason):
-        try:
-            from_string = self.hs.config.email_notif_from % {
-                "app": self.app_name
-            }
-        except TypeError:
-            from_string = self.hs.config.email_notif_from
+    def send_password_reset_mail(
+        self,
+        email_address,
+        token,
+        client_secret,
+        sid,
+    ):
+        """Send an email with a password reset link to a user
+
+        Args:
+            email_address (str): Email address we're sending the password
+                reset to
+            token (str): Unique token generated by the server to verify
+                password reset email was received
+            client_secret (str): Unique token generated by the client to
+                group together multiple email sending attempts
+            sid (str): The generated session ID
+        """
+        if email.utils.parseaddr(email_address)[1] == '':
+            raise RuntimeError("Invalid 'to' email address")
+
+        link = (
+            self.hs.config.public_baseurl +
+            "_synapse/password_reset/email/submit_token"
+            "?token=%s&client_secret=%s&sid=%s" %
+            (token, client_secret, sid)
+        )
 
-        raw_from = email.utils.parseaddr(from_string)[1]
-        raw_to = email.utils.parseaddr(email_address)[1]
+        template_vars = {
+            "link": link,
+        }
 
-        if raw_to == '':
-            raise RuntimeError("Invalid 'to' address")
+        yield self.send_email(
+            email_address,
+            "[%s] Password Reset Email" % self.hs.config.server_name,
+            template_vars,
+        )
 
+    @defer.inlineCallbacks
+    def send_notification_mail(self, app_id, user_id, email_address,
+                               push_actions, reason):
+        """Send email regarding a user's room notifications"""
         rooms_in_order = deduped_ordered_list(
             [pa['room_id'] for pa in push_actions]
         )
@@ -176,14 +203,36 @@ class Mailer(object):
             "reason": reason,
         }
 
-        html_text = self.notif_template_html.render(**template_vars)
+        yield self.send_email(
+            email_address,
+            "[%s] %s" % (self.app_name, summary_text),
+            template_vars,
+        )
+
+    @defer.inlineCallbacks
+    def send_email(self, email_address, subject, template_vars):
+        """Send an email with the given information and template text"""
+        try:
+            from_string = self.hs.config.email_notif_from % {
+                "app": self.app_name
+            }
+        except TypeError:
+            from_string = self.hs.config.email_notif_from
+
+        raw_from = email.utils.parseaddr(from_string)[1]
+        raw_to = email.utils.parseaddr(email_address)[1]
+
+        if raw_to == '':
+            raise RuntimeError("Invalid 'to' address")
+
+        html_text = self.template_html.render(**template_vars)
         html_part = MIMEText(html_text, "html", "utf8")
 
-        plain_text = self.notif_template_text.render(**template_vars)
+        plain_text = self.template_text.render(**template_vars)
         text_part = MIMEText(plain_text, "plain", "utf8")
 
         multipart_msg = MIMEMultipart('alternative')
-        multipart_msg['Subject'] = "[%s] %s" % (self.app_name, summary_text)
+        multipart_msg['Subject'] = subject
         multipart_msg['From'] = from_string
         multipart_msg['To'] = email_address
         multipart_msg['Date'] = email.utils.formatdate()
diff --git a/synapse/push/pusher.py b/synapse/push/pusher.py
index 14bc7823cf..aff85daeb5 100644
--- a/synapse/push/pusher.py
+++ b/synapse/push/pusher.py
@@ -70,8 +70,8 @@ class PusherFactory(object):
             mailer = Mailer(
                 hs=self.hs,
                 app_name=app_name,
-                notif_template_html=self.notif_template_html,
-                notif_template_text=self.notif_template_text,
+                template_html=self.notif_template_html,
+                template_text=self.notif_template_text,
             )
             self.mailers[app_name] = mailer
         return EmailPusher(self.hs, pusherdict, mailer)