Improve login form handling errors (#93)

* Pass username/identifier to InvalidCredentials
* Allow hiding NoSuchUser error

Author: OmeGak

CHANGES.rst

@@ -7,6 +7,10 @@ Version 0.7
 - Support multiple id fields in SAML identity provider
 - Include ``client_id`` in authlib logout URL since some OIDC providers mayrequire this
 - Allow setting timeout for authlib token requests (default: 10 seconds)
+- Add new ``MULTIPASS_HIDE_NO_SUCH_USER`` config setting to convert ``NoSuchUser``
+  exceptions to ``InvalidCredentials`` to avoid disclosing whether a username is valid
+- Include the username in the ``identifier`` attribute of the ``InvalidCredentials``
+  exception so applications can apply e.g. per-username rate limiting
 
 Version 0.6
 -----------

docs/quickstart.rst

@@ -54,6 +54,7 @@ The following configuration values exist for Flask-Multipass:
 ``MULTIPASS_FAILURE_CATEGORY``         Category of message when flashing after unsuccessful login
 ``MULTIPASS_ALL_MATCHING_IDENTITIES``  If true, all matching identities are passed after successful authentication
 ``MULTIPASS_REQUIRE_IDENTITY``         If true, ``IdentityRetrievalFailed`` is raised when no matching identities are found, otherwise empty list is passed
+``MULTIPASS_HIDE_NO_SUCH_USER``        If true, ``InvalidCredentials`` instead of ``NoSuchUser`` is raised when no user is found in the system
 ====================================== =========================================
 
 A configuration example can be found here: :ref:`config_example`

flask_multipass/core.py

@@ -12,7 +12,13 @@
 from werkzeug.exceptions import NotFound
 
 from flask_multipass.auth import AuthProvider
-from flask_multipass.exceptions import GroupRetrievalFailed, IdentityRetrievalFailed, MultipassException
+from flask_multipass.exceptions import (
+    GroupRetrievalFailed,
+    IdentityRetrievalFailed,
+    InvalidCredentials,
+    MultipassException,
+    NoSuchUser,
+)
 from flask_multipass.identity import IdentityProvider
 from flask_multipass.util import (
     get_canonical_provider_map,
@@ -72,6 +78,7 @@ def init_app(self, app):
         app.config.setdefault('MULTIPASS_FAILURE_CATEGORY', 'error')
         app.config.setdefault('MULTIPASS_ALL_MATCHING_IDENTITIES', False)
         app.config.setdefault('MULTIPASS_REQUIRE_IDENTITY', True)
+        app.config.setdefault('MULTIPASS_HIDE_NO_SUCH_USER', False)
         with app.app_context():
             self._create_login_rule()
             state.auth_providers = ImmutableDict(self._create_providers('AUTH', AuthProvider))
@@ -528,6 +535,8 @@ def handle_login_form(self, provider, data):
         try:
             response = provider.process_local_login(data)
         except MultipassException as e:
+            if isinstance(e, NoSuchUser) and current_app.config['MULTIPASS_HIDE_NO_SUCH_USER']:
+                e = InvalidCredentials(e.provider)
             self.handle_auth_error(e)
         else:
             return response

flask_multipass/exceptions.py

@@ -32,8 +32,9 @@ def __init__(self, details=None, provider=None):
 class InvalidCredentials(AuthenticationFailed):
     """Indicates a failure to authenticate using the given credentials."""
 
-    def __init__(self, details=None, provider=None):
+    def __init__(self, details=None, provider=None, identifier=None):
         AuthenticationFailed.__init__(self, 'Invalid credentials', details=details, provider=provider)
+        self.identifier = identifier
 
 
 class IdentityRetrievalFailed(MultipassException):

flask_multipass/providers/ldap/providers.py

@@ -81,7 +81,7 @@ def process_local_login(self, data):
                     raise NoSuchUser(provider=self)
                 current_ldap.connection.simple_bind_s(user_dn, password)
             except INVALID_CREDENTIALS:
-                raise InvalidCredentials(provider=self)
+                raise InvalidCredentials(provider=self, identifier=data['username'])
         auth_info = AuthInfo(self, identifier=user_data[self.ldap_settings['uid']][0])
         return self.multipass.handle_auth_success(auth_info)
 

flask_multipass/providers/sqlalchemy.py

@@ -55,7 +55,7 @@ def process_local_login(self, data):
         if not identity:
             raise NoSuchUser(provider=self)
         if not self.check_password(identity, data['password']):
-            raise InvalidCredentials(provider=self)
+            raise InvalidCredentials(provider=self, identifier=data['identifier'])
         auth_info = AuthInfo(self, identity=identity)
         return self.multipass.handle_auth_success(auth_info)
 

flask_multipass/providers/static.py

@@ -44,7 +44,7 @@ def process_local_login(self, data):
         if password is None:
             raise NoSuchUser(provider=self)
         if password != data['password']:
-            raise InvalidCredentials(provider=self)
+            raise InvalidCredentials(provider=self, identifier=data['username'])
         auth_info = AuthInfo(self, username=data['username'])
         return self.multipass.handle_auth_success(auth_info)