ConsentResource to gather policy consent from users

Hopefully there are enough comments and docs in this that it makes sense on its
own.

synapse/rest/consent/consent_resource.py

@@ -0,0 +1,210 @@
+# -*- coding: utf-8 -*-
+# Copyright 2018 New Vector Ltd
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from hashlib import sha256
+import hmac
+import logging
+from os import path
+from six.moves import http_client
+
+import jinja2
+from jinja2 import TemplateNotFound
+from twisted.internet import defer
+from twisted.web.resource import Resource
+from twisted.web.server import NOT_DONE_YET
+
+from synapse.api.errors import NotFoundError, SynapseError, StoreError
+from synapse.config import ConfigError
+from synapse.http.server import (
+    finish_request,
+    wrap_html_request_handler,
+)
+from synapse.http.servlet import parse_string
+from synapse.types import UserID
+
+
+# language to use for the templates. TODO: figure this out from Accept-Language
+TEMPLATE_LANGUAGE = "en"
+
+logger = logging.getLogger(__name__)
+
+# use hmac.compare_digest if we have it (python 2.7.7), else just use equality
+if hasattr(hmac, "compare_digest"):
+    compare_digest = hmac.compare_digest
+else:
+    def compare_digest(a, b):
+        return a == b
+
+
+class ConsentResource(Resource):
+    """A twisted Resource to display a privacy policy and gather consent to it
+
+    When accessed via GET, returns the privacy policy via a template.
+
+    When accessed via POST, records the user's consent in the database and
+    displays a success page.
+
+    The config should include a template_dir setting which contains templates
+    for the HTML. The directory should contain one subdirectory per language
+    (eg, 'en', 'fr'), and each language directory should contain the policy
+    document (named as '<version>.html') and a success page (success.html).
+
+    Both forms take a set of parameters from the browser. For the POST form,
+    these are normally sent as form parameters (but may be query-params); for
+    GET requests they must be query params. These are:
+
+        u: the complete mxid, or the localpart of the user giving their
+           consent. Required for both GET (where it is used as an input to the
+           template) and for POST (where it is used to find the row in the db
+           to update).
+
+        h: hmac_sha256(secret, u), where 'secret' is the privacy_secret in the
+           config file. If it doesn't match, the request is 403ed.
+
+        v: the version of the privacy policy being agreed to.
+
+           For GET: optional, and defaults to whatever was set in the config
+           file. Used to choose the version of the policy to pick from the
+           templates directory.
+
+           For POST: required; gives the value to be recorded in the database
+           against the user.
+    """
+    def __init__(self, hs):
+        """
+        Args:
+            hs (synapse.server.HomeServer): homeserver
+        """
+        Resource.__init__(self)
+
+        self.hs = hs
+        self.store = hs.get_datastore()
+
+        # this is required by the request_handler wrapper
+        self.clock = hs.get_clock()
+
+        consent_config = hs.config.consent_config
+        if consent_config is None:
+            raise ConfigError(
+                "Consent resource is enabled but user_consent section is "
+                "missing in config file.",
+            )
+
+        # daemonize changes the cwd to /, so make the path absolute now.
+        consent_template_directory = path.abspath(
+            consent_config["template_dir"],
+        )
+        if not path.isdir(consent_template_directory):
+            raise ConfigError(
+                "Could not find template directory '%s'" % (
+                    consent_template_directory,
+                ),
+            )
+
+        loader = jinja2.FileSystemLoader(consent_template_directory)
+        self._jinja_env = jinja2.Environment(loader=loader)
+
+        self._default_consent_verison = consent_config["default_version"]
+
+        if hs.config.form_secret is None:
+            raise ConfigError(
+                "Consent resource is enabled but form_secret is not set in "
+                "config file. It should be set to an arbitrary secret string.",
+            )
+
+        self._hmac_secret = hs.config.form_secret.encode("utf-8")
+
+    def render_GET(self, request):
+        self._async_render_GET(request)
+        return NOT_DONE_YET
+
+    @wrap_html_request_handler
+    def _async_render_GET(self, request):
+        """
+        Args:
+            request (twisted.web.http.Request):
+        """
+
+        version = parse_string(request, "v",
+                               default=self._default_consent_verison)
+        username = parse_string(request, "u", required=True)
+        userhmac = parse_string(request, "h", required=True)
+
+        self._check_hash(username, userhmac)
+
+        try:
+            self._render_template(
+                request, "%s.html" % (version,),
+                user=username, userhmac=userhmac, version=version,
+            )
+        except TemplateNotFound:
+            raise NotFoundError("Unknown policy version")
+
+    def render_POST(self, request):
+        self._async_render_POST(request)
+        return NOT_DONE_YET
+
+    @wrap_html_request_handler
+    @defer.inlineCallbacks
+    def _async_render_POST(self, request):
+        """
+        Args:
+            request (twisted.web.http.Request):
+        """
+        version = parse_string(request, "v", required=True)
+        username = parse_string(request, "u", required=True)
+        userhmac = parse_string(request, "h", required=True)
+
+        self._check_hash(username, userhmac)
+
+        if username.startswith('@'):
+            qualified_user_id = username
+        else:
+            qualified_user_id = UserID(username, self.hs.hostname).to_string()
+
+        try:
+            yield self.store.user_set_consent_version(qualified_user_id, version)
+        except StoreError as e:
+            if e.code != 404:
+                raise
+            raise NotFoundError("Unknown user")
+
+        try:
+            self._render_template(request, "success.html")
+        except TemplateNotFound:
+            raise NotFoundError("success.html not found")
+
+    def _render_template(self, request, template_name, **template_args):
+        # get_template checks for ".." so we don't need to worry too much
+        # about path traversal here.
+        template_html = self._jinja_env.get_template(
+            path.join(TEMPLATE_LANGUAGE, template_name)
+        )
+        html_bytes = template_html.render(**template_args).encode("utf8")
+
+        request.setHeader(b"Content-Type", b"text/html; charset=utf-8")
+        request.setHeader(b"Content-Length", b"%i" % len(html_bytes))
+        request.write(html_bytes)
+        finish_request(request)
+
+    def _check_hash(self, userid, userhmac):
+        want_mac = hmac.new(
+            key=self._hmac_secret,
+            msg=userid,
+            digestmod=sha256,
+        ).hexdigest()
+
+        if not compare_digest(want_mac, userhmac):
+            raise SynapseError(http_client.FORBIDDEN, "HMAC incorrect")