Fix-up CAS code to always require a public baseurl.

synapse/config/cas.py

@@ -31,20 +31,21 @@ def read_config(self, config, **kwargs):
         if self.cas_enabled:
             self.cas_server_url = cas_config["server_url"]
 
-            # If the service_url is given, use it for backwards compatibility.
-            # Otherwise, use the public_baseurl.
-            public_base_url = cas_config.get("service_url") or self.public_baseurl
-            if not public_base_url:
+            # The public baseurl is required because it is used by the redirect
+            # template.
+            public_baseurl = self.public_baseurl
+            if not public_baseurl:
                 raise ConfigError("cas_config requires a public_baseurl to be set")
 
-            # If the service_url was given, ensure it doesn't have an extra slash.
-            if public_base_url[-1] != "/":
-                public_base_url += "/"
+            # If the service_url is given, use it for backwards compatibility.
+            # Otherwise, use the public_baseurl.
+            if cas_config.get("service_url"):
+                public_baseurl = cas_config["service_url"]
+                if public_baseurl[-1] != "/":
+                    public_baseurl += "/"
 
             # TODO Update this to a _synapse URL.
-            self.cas_service_url = (
-                public_base_url + "_matrix/client/r0/login/cas/ticket"
-            )
+            self.cas_service_url = public_baseurl + "_matrix/client/r0/login/cas/ticket"
             self.cas_displayname_attribute = cas_config.get("displayname_attribute")
             self.cas_required_attributes = cas_config.get("required_attributes") or {}
         else:

tests/rest/client/v1/test_login.py

@@ -672,10 +672,12 @@ def make_homeserver(self, reactor, clock):
         self.redirect_path = "_synapse/client/login/sso/redirect/confirm"
 
         config = self.default_config()
+        config["public_baseurl"] = (
+            config.get("public_baseurl") or "https://matrix.goodserver.com:8448"
+        )
         config["cas_config"] = {
             "enabled": True,
             "server_url": CAS_SERVER,
-            "service_url": "https://matrix.goodserver.com:8448",
         }
 
         cas_user_id = "username"