support custom login types for validating users

Wire the custom login type support from password providers into the UI-auth
user-validation flows.

synapse/handlers/auth.py

@@ -49,7 +49,6 @@ class AuthHandler(BaseHandler):
         """
         super(AuthHandler, self).__init__(hs)
         self.checkers = {
-            LoginType.PASSWORD: self._check_password_auth,
             LoginType.RECAPTCHA: self._check_recaptcha,
             LoginType.EMAIL_IDENTITY: self._check_email_identity,
             LoginType.MSISDN: self._check_msisdn,
@@ -78,15 +77,20 @@ class AuthHandler(BaseHandler):
         self.macaroon_gen = hs.get_macaroon_generator()
         self._password_enabled = hs.config.password_enabled
 
-        login_types = set()
+        # we keep this as a list despite the O(N^2) implication so that we can
+        # keep PASSWORD first and avoid confusing clients which pick the first
+        # type in the list. (NB that the spec doesn't require us to do so and
+        # clients which favour types that they don't understand over those that
+        # they do are technically broken)
+        login_types = []
         if self._password_enabled:
-            login_types.add(LoginType.PASSWORD)
+            login_types.append(LoginType.PASSWORD)
         for provider in self.password_providers:
             if hasattr(provider, "get_supported_login_types"):
-                login_types.update(
-                    provider.get_supported_login_types().keys()
-                )
-        self._supported_login_types = frozenset(login_types)
+                for t in provider.get_supported_login_types().keys():
+                    if t not in login_types:
+                        login_types.append(t)
+        self._supported_login_types = login_types
 
     @defer.inlineCallbacks
     def validate_user_via_ui_auth(self, requester, request_body, clientip):
@@ -116,14 +120,27 @@ class AuthHandler(BaseHandler):
                 a different user to `requester`
         """
 
-        # we only support password login here
-        flows = [[LoginType.PASSWORD]]
+        # build a list of supported flows
+        flows = [
+            [login_type] for login_type in self._supported_login_types
+        ]
 
         result, params, _ = yield self.check_auth(
             flows, request_body, clientip,
         )
 
-        user_id = result[LoginType.PASSWORD]
+        # find the completed login type
+        for login_type in self._supported_login_types:
+            if login_type not in result:
+                continue
+
+            user_id = result[login_type]
+            break
+        else:
+            # this can't happen
+            raise Exception(
+                "check_auth returned True but no successful login type",
+            )
 
         # check that the UI auth matched the access token
         if user_id != requester.user.to_string():
@@ -210,14 +227,12 @@ class AuthHandler(BaseHandler):
         errordict = {}
         if 'type' in authdict:
             login_type = authdict['type']
-            if login_type not in self.checkers:
-                raise LoginError(400, "", Codes.UNRECOGNIZED)
             try:
-                result = yield self.checkers[login_type](authdict, clientip)
+                result = yield self._check_auth_dict(authdict, clientip)
                 if result:
                     creds[login_type] = result
                     self._save_session(session)
-            except LoginError, e:
+            except LoginError as e:
                 if login_type == LoginType.EMAIL_IDENTITY:
                     # riot used to have a bug where it would request a new
                     # validation token (thus sending a new email) each time it
@@ -226,7 +241,7 @@ class AuthHandler(BaseHandler):
                     #
                     # Grandfather in the old behaviour for now to avoid
                     # breaking old riot deployments.
-                    raise e
+                    raise
 
                 # this step failed. Merge the error dict into the response
                 # so that the client can have another go.
@@ -323,17 +338,35 @@ class AuthHandler(BaseHandler):
         return sess.setdefault('serverdict', {}).get(key, default)
 
     @defer.inlineCallbacks
-    def _check_password_auth(self, authdict, _):
-        if "user" not in authdict or "password" not in authdict:
-            raise LoginError(400, "", Codes.MISSING_PARAM)
+    def _check_auth_dict(self, authdict, clientip):
+        """Attempt to validate the auth dict provided by a client
 
-        user_id = authdict["user"]
-        password = authdict["password"]
+        Args:
+            authdict (object): auth dict provided by the client
+            clientip (str): IP address of the client
 
-        (canonical_id, callback) = yield self.validate_login(user_id, {
-            "type": LoginType.PASSWORD,
-            "password": password,
-        })
+        Returns:
+            Deferred: result of the stage verification.
+
+        Raises:
+            StoreError if there was a problem accessing the database
+            SynapseError if there was a problem with the request
+            LoginError if there was an authentication problem.
+        """
+        login_type = authdict['type']
+        checker = self.checkers.get(login_type)
+        if checker is not None:
+            res = yield checker(authdict, clientip)
+            defer.returnValue(res)
+
+        # build a v1-login-style dict out of the authdict and fall back to the
+        # v1 code
+        user_id = authdict.get("user")
+
+        if user_id is None:
+            raise SynapseError(400, "", Codes.MISSING_PARAM)
+
+        (canonical_id, callback) = yield self.validate_login(user_id, authdict)
         defer.returnValue(canonical_id)
 
     @defer.inlineCallbacks