Complete the SAML2 implementation (#5422)

* SAML2 Improvements and redirect stuff

Signed-off-by: Alexander Trost <galexrt@googlemail.com>

* Code cleanups and simplifications.

Also: share the saml client between redirect and response handlers.

* changelog

* Revert redundant changes to static js

* Move all the saml stuff out to a centralised handler

* Add support for tracking SAML2 sessions.

This allows us to correctly handle `allow_unsolicited: False`.

* update sample config

* cleanups

* update sample config

* rename BaseSSORedirectServlet for consistency

* Address review comments

2 files changed, 48 insertions, 43 deletions

diff --git a/synapse/rest/client/v1/login.py b/synapse/rest/client/v1/login.py
index e88d2ad7bd..f961178235 100644
--- a/synapse/rest/client/v1/login.py
+++ b/synapse/rest/client/v1/login.py
@@ -86,6 +86,7 @@ class LoginRestServlet(RestServlet):
         self.jwt_enabled = hs.config.jwt_enabled
         self.jwt_secret = hs.config.jwt_secret
         self.jwt_algorithm = hs.config.jwt_algorithm
+        self.saml2_enabled = hs.config.saml2_enabled
         self.cas_enabled = hs.config.cas_enabled
         self.auth_handler = self.hs.get_auth_handler()
         self.registration_handler = hs.get_registration_handler()
@@ -97,6 +98,9 @@ class LoginRestServlet(RestServlet):
         flows = []
         if self.jwt_enabled:
             flows.append({"type": LoginRestServlet.JWT_TYPE})
+        if self.saml2_enabled:
+            flows.append({"type": LoginRestServlet.SSO_TYPE})
+            flows.append({"type": LoginRestServlet.TOKEN_TYPE})
         if self.cas_enabled:
             flows.append({"type": LoginRestServlet.SSO_TYPE})
 
@@ -351,27 +355,49 @@ class LoginRestServlet(RestServlet):
         defer.returnValue(result)
 
 
-class CasRedirectServlet(RestServlet):
+class BaseSSORedirectServlet(RestServlet):
+    """Common base class for /login/sso/redirect impls"""
+
     PATTERNS = client_patterns("/login/(cas|sso)/redirect", v1=True)
 
+    def on_GET(self, request):
+        args = request.args
+        if b"redirectUrl" not in args:
+            return 400, "Redirect URL not specified for SSO auth"
+        client_redirect_url = args[b"redirectUrl"][0]
+        sso_url = self.get_sso_url(client_redirect_url)
+        request.redirect(sso_url)
+        finish_request(request)
+
+    def get_sso_url(self, client_redirect_url):
+        """Get the URL to redirect to, to perform SSO auth
+
+        Args:
+            client_redirect_url (bytes): the URL that we should redirect the
+                client to when everything is done
+
+        Returns:
+            bytes: URL to redirect to
+        """
+        # to be implemented by subclasses
+        raise NotImplementedError()
+
+
+class CasRedirectServlet(BaseSSORedirectServlet):
     def __init__(self, hs):
         super(CasRedirectServlet, self).__init__()
         self.cas_server_url = hs.config.cas_server_url.encode("ascii")
         self.cas_service_url = hs.config.cas_service_url.encode("ascii")
 
-    def on_GET(self, request):
-        args = request.args
-        if b"redirectUrl" not in args:
-            return (400, "Redirect URL not specified for CAS auth")
+    def get_sso_url(self, client_redirect_url):
         client_redirect_url_param = urllib.parse.urlencode(
-            {b"redirectUrl": args[b"redirectUrl"][0]}
+            {b"redirectUrl": client_redirect_url}
         ).encode("ascii")
         hs_redirect_url = self.cas_service_url + b"/_matrix/client/r0/login/cas/ticket"
         service_param = urllib.parse.urlencode(
             {b"service": b"%s?%s" % (hs_redirect_url, client_redirect_url_param)}
         ).encode("ascii")
-        request.redirect(b"%s/login?%s" % (self.cas_server_url, service_param))
-        finish_request(request)
+        return b"%s/login?%s" % (self.cas_server_url, service_param)
 
 
 class CasTicketServlet(RestServlet):
@@ -454,6 +480,16 @@ class CasTicketServlet(RestServlet):
         return user, attributes
 
 
+class SAMLRedirectServlet(BaseSSORedirectServlet):
+    PATTERNS = client_patterns("/login/sso/redirect", v1=True)
+
+    def __init__(self, hs):
+        self._saml_handler = hs.get_saml_handler()
+
+    def get_sso_url(self, client_redirect_url):
+        return self._saml_handler.handle_redirect_request(client_redirect_url)
+
+
 class SSOAuthHandler(object):
     """
     Utility class for Resources and Servlets which handle the response from a SSO
@@ -529,3 +565,5 @@ def register_servlets(hs, http_server):
     if hs.config.cas_enabled:
         CasRedirectServlet(hs).register(http_server)
         CasTicketServlet(hs).register(http_server)
+    elif hs.config.saml2_enabled:
+        SAMLRedirectServlet(hs).register(http_server)
diff --git a/synapse/rest/saml2/response_resource.py b/synapse/rest/saml2/response_resource.py
index 939c87306c..69ecc5e4b4 100644
--- a/synapse/rest/saml2/response_resource.py
+++ b/synapse/rest/saml2/response_resource.py
@@ -13,17 +13,8 @@
 # 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.
-import logging
 
-import saml2
-from saml2.client import Saml2Client
-
-from synapse.api.errors import CodeMessageException
 from synapse.http.server import DirectServeResource, wrap_html_request_handler
-from synapse.http.servlet import parse_string
-from synapse.rest.client.v1.login import SSOAuthHandler
-
-logger = logging.getLogger(__name__)
 
 
 class SAML2ResponseResource(DirectServeResource):
@@ -33,32 +24,8 @@ class SAML2ResponseResource(DirectServeResource):
 
     def __init__(self, hs):
         super().__init__()
-
-        self._saml_client = Saml2Client(hs.config.saml2_sp_config)
-        self._sso_auth_handler = SSOAuthHandler(hs)
+        self._saml_handler = hs.get_saml_handler()
 
     @wrap_html_request_handler
     async def _async_render_POST(self, request):
-        resp_bytes = parse_string(request, "SAMLResponse", required=True)
-        relay_state = parse_string(request, "RelayState", required=True)
-
-        try:
-            saml2_auth = self._saml_client.parse_authn_request_response(
-                resp_bytes, saml2.BINDING_HTTP_POST
-            )
-        except Exception as e:
-            logger.warning("Exception parsing SAML2 response", exc_info=1)
-            raise CodeMessageException(400, "Unable to parse SAML2 response: %s" % (e,))
-
-        if saml2_auth.not_signed:
-            raise CodeMessageException(400, "SAML2 response was not signed")
-
-        if "uid" not in saml2_auth.ava:
-            raise CodeMessageException(400, "uid not in SAML2 response")
-
-        username = saml2_auth.ava["uid"][0]
-
-        displayName = saml2_auth.ava.get("displayName", [None])[0]
-        return self._sso_auth_handler.on_successful_auth(
-            username, request, relay_state, user_display_name=displayName
-        )
+        return await self._saml_handler.handle_saml_response(request)