Refactor some logic from LoginRestServlet into AuthHandler

I'm going to need some more flexibility in handling login types in password
auth providers, so as a first step, move some stuff from LoginRestServlet into
AuthHandler.

In particular, we pass everything other than SAML, JWT and token logins down to
the AuthHandler, which now has responsibility for checking the login type and
fishing the password out of the login dictionary, as well as qualifying the
user_id if need be. Ideally SAML, JWT and token would go that way too, but
there's no real need for it right now and I'm trying to minimise impact.

This commit *should* be non-functional.

2 files changed, 78 insertions, 57 deletions

diff --git a/synapse/handlers/auth.py b/synapse/handlers/auth.py
index acae4d9e0d..93d8ac0e04 100644
--- a/synapse/handlers/auth.py
+++ b/synapse/handlers/auth.py
@@ -77,6 +77,12 @@ class AuthHandler(BaseHandler):
         self.hs = hs  # FIXME better possibility to access registrationHandler later?
         self.device_handler = hs.get_device_handler()
         self.macaroon_gen = hs.get_macaroon_generator()
+        self._password_enabled = hs.config.password_enabled
+
+        login_types = set()
+        if self._password_enabled:
+            login_types.add(LoginType.PASSWORD)
+        self._supported_login_types = frozenset(login_types)
 
     @defer.inlineCallbacks
     def check_auth(self, flows, clientdict, clientip):
@@ -266,10 +272,11 @@ class AuthHandler(BaseHandler):
 
         user_id = authdict["user"]
         password = authdict["password"]
-        if not user_id.startswith('@'):
-            user_id = UserID(user_id, self.hs.hostname).to_string()
 
-        return self._check_password(user_id, password)
+        return self.validate_login(user_id, {
+            "type": LoginType.PASSWORD,
+            "password": password,
+        })
 
     @defer.inlineCallbacks
     def _check_recaptcha(self, authdict, clientip):
@@ -398,23 +405,6 @@ class AuthHandler(BaseHandler):
 
         return self.sessions[session_id]
 
-    def validate_password_login(self, user_id, password):
-        """
-        Authenticates the user with their username and password.
-
-        Used only by the v1 login API.
-
-        Args:
-            user_id (str): complete @user:id
-            password (str): Password
-        Returns:
-            defer.Deferred: (str) canonical user id
-        Raises:
-            StoreError if there was a problem accessing the database
-            LoginError if there was an authentication problem.
-        """
-        return self._check_password(user_id, password)
-
     @defer.inlineCallbacks
     def get_access_token_for_user_id(self, user_id, device_id=None,
                                      initial_display_name=None):
@@ -501,26 +491,60 @@ class AuthHandler(BaseHandler):
             )
         defer.returnValue(result)
 
+    def get_supported_login_types(self):
+        """Get a the login types supported for the /login API
+
+        By default this is just 'm.login.password' (unless password_enabled is
+        False in the config file), but password auth providers can provide
+        other login types.
+
+        Returns:
+            Iterable[str]: login types
+        """
+        return self._supported_login_types
+
     @defer.inlineCallbacks
-    def _check_password(self, user_id, password):
-        """Authenticate a user against the LDAP and local databases.
+    def validate_login(self, user_id, login_submission):
+        """Authenticates the user for the /login API
 
-        user_id is checked case insensitively against the local database, but
-        will throw if there are multiple inexact matches.
+        Also used by the user-interactive auth flow to validate
+        m.login.password auth types.
 
         Args:
-            user_id (str): complete @user:id
+            user_id (str): user_id supplied by the user
+            login_submission (dict): the whole of the login submission
+                (including 'type' and other relevant fields)
         Returns:
-            (str) the canonical_user_id
+            Deferred[str]: canonical user id
         Raises:
-            LoginError if login fails
+            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.
         """
+
+        if not user_id.startswith('@'):
+            user_id = UserID(
+                user_id, self.hs.hostname
+            ).to_string()
+
+        login_type = login_submission.get("type")
+
+        if login_type != LoginType.PASSWORD:
+            raise SynapseError(400, "Bad login type.")
+        if not self._password_enabled:
+            raise SynapseError(400, "Password login has been disabled.")
+        if "password" not in login_submission:
+            raise SynapseError(400, "Missing parameter: password")
+
+        password = login_submission["password"]
         for provider in self.password_providers:
             is_valid = yield provider.check_password(user_id, password)
             if is_valid:
                 defer.returnValue(user_id)
 
-        canonical_user_id = yield self._check_local_password(user_id, password)
+        canonical_user_id = yield self._check_local_password(
+            user_id, password,
+        )
 
         if canonical_user_id:
             defer.returnValue(canonical_user_id)
diff --git a/synapse/rest/client/v1/login.py b/synapse/rest/client/v1/login.py
index 9536e8ade6..d24590011b 100644
--- a/synapse/rest/client/v1/login.py
+++ b/synapse/rest/client/v1/login.py
@@ -85,7 +85,6 @@ def login_id_thirdparty_from_phone(identifier):
 
 class LoginRestServlet(ClientV1RestServlet):
     PATTERNS = client_path_patterns("/login$")
-    PASS_TYPE = "m.login.password"
     SAML2_TYPE = "m.login.saml2"
     CAS_TYPE = "m.login.cas"
     TOKEN_TYPE = "m.login.token"
@@ -94,7 +93,6 @@ class LoginRestServlet(ClientV1RestServlet):
     def __init__(self, hs):
         super(LoginRestServlet, self).__init__(hs)
         self.idp_redirect_url = hs.config.saml2_idp_redirect_url
-        self.password_enabled = hs.config.password_enabled
         self.saml2_enabled = hs.config.saml2_enabled
         self.jwt_enabled = hs.config.jwt_enabled
         self.jwt_secret = hs.config.jwt_secret
@@ -121,8 +119,10 @@ class LoginRestServlet(ClientV1RestServlet):
             # fall back to the fallback API if they don't understand one of the
             # login flow types returned.
             flows.append({"type": LoginRestServlet.TOKEN_TYPE})
-        if self.password_enabled:
-            flows.append({"type": LoginRestServlet.PASS_TYPE})
+
+        flows.extend((
+            {"type": t} for t in self.auth_handler.get_supported_login_types()
+        ))
 
         return (200, {"flows": flows})
 
@@ -133,14 +133,8 @@ class LoginRestServlet(ClientV1RestServlet):
     def on_POST(self, request):
         login_submission = parse_json_object_from_request(request)
         try:
-            if login_submission["type"] == LoginRestServlet.PASS_TYPE:
-                if not self.password_enabled:
-                    raise SynapseError(400, "Password login has been disabled.")
-
-                result = yield self.do_password_login(login_submission)
-                defer.returnValue(result)
-            elif self.saml2_enabled and (login_submission["type"] ==
-                                         LoginRestServlet.SAML2_TYPE):
+            if self.saml2_enabled and (login_submission["type"] ==
+                                       LoginRestServlet.SAML2_TYPE):
                 relay_state = ""
                 if "relay_state" in login_submission:
                     relay_state = "&RelayState=" + urllib.quote(
@@ -157,15 +151,21 @@ class LoginRestServlet(ClientV1RestServlet):
                 result = yield self.do_token_login(login_submission)
                 defer.returnValue(result)
             else:
-                raise SynapseError(400, "Bad login type.")
+                result = yield self._do_other_login(login_submission)
+                defer.returnValue(result)
         except KeyError:
             raise SynapseError(400, "Missing JSON keys.")
 
     @defer.inlineCallbacks
-    def do_password_login(self, login_submission):
-        if "password" not in login_submission:
-            raise SynapseError(400, "Missing parameter: password")
+    def _do_other_login(self, login_submission):
+        """Handle non-token/saml/jwt logins
 
+        Args:
+            login_submission:
+
+        Returns:
+            (int, object): HTTP code/response
+        """
         login_submission_legacy_convert(login_submission)
 
         if "identifier" not in login_submission:
@@ -208,25 +208,22 @@ class LoginRestServlet(ClientV1RestServlet):
         if "user" not in identifier:
             raise SynapseError(400, "User identifier is missing 'user' key")
 
-        user_id = identifier["user"]
-
-        if not user_id.startswith('@'):
-            user_id = UserID(
-                user_id, self.hs.hostname
-            ).to_string()
-
         auth_handler = self.auth_handler
-        user_id = yield auth_handler.validate_password_login(
-            user_id=user_id,
-            password=login_submission["password"],
+        canonical_user_id = yield auth_handler.validate_login(
+            identifier["user"],
+            login_submission,
+        )
+
+        device_id = yield self._register_device(
+            canonical_user_id, login_submission,
         )
-        device_id = yield self._register_device(user_id, login_submission)
         access_token = yield auth_handler.get_access_token_for_user_id(
-            user_id, device_id,
+            canonical_user_id, device_id,
             login_submission.get("initial_device_display_name"),
         )
+
         result = {
-            "user_id": user_id,  # may have changed
+            "user_id": canonical_user_id,
             "access_token": access_token,
             "home_server": self.hs.hostname,
             "device_id": device_id,