Merge pull request #1155 from matrix-org/erikj/pluggable_pwd_auth

Implement pluggable password auth

5 files changed, 471 insertions, 398 deletions

diff --git a/synapse/config/homeserver.py b/synapse/config/homeserver.py
index 79b0534b3b..0f890fc04a 100644
--- a/synapse/config/homeserver.py
+++ b/synapse/config/homeserver.py
@@ -30,7 +30,7 @@ from .saml2 import SAML2Config
 from .cas import CasConfig
 from .password import PasswordConfig
 from .jwt import JWTConfig
-from .ldap import LDAPConfig
+from .password_auth_providers import PasswordAuthProviderConfig
 from .emailconfig import EmailConfig
 from .workers import WorkerConfig
 
@@ -39,8 +39,8 @@ class HomeServerConfig(TlsConfig, ServerConfig, DatabaseConfig, LoggingConfig,
                        RatelimitConfig, ContentRepositoryConfig, CaptchaConfig,
                        VoipConfig, RegistrationConfig, MetricsConfig, ApiConfig,
                        AppServiceConfig, KeyConfig, SAML2Config, CasConfig,
-                       JWTConfig, LDAPConfig, PasswordConfig, EmailConfig,
-                       WorkerConfig,):
+                       JWTConfig, PasswordConfig, EmailConfig,
+                       WorkerConfig, PasswordAuthProviderConfig,):
     pass
 
 
diff --git a/synapse/config/ldap.py b/synapse/config/ldap.py
deleted file mode 100644
index d83c2230be..0000000000
--- a/synapse/config/ldap.py
+++ /dev/null
@@ -1,100 +0,0 @@
-# -*- coding: utf-8 -*-
-# Copyright 2015 Niklas Riekenbrauck
-#
-# Licensed under the Apache License, Version 2.0 (the "License");
-# you may not use this file except in compliance with the License.
-# You may obtain a copy of the License at
-#
-#     http://www.apache.org/licenses/LICENSE-2.0
-#
-# Unless required by applicable law or agreed to in writing, software
-# distributed under the License is distributed on an "AS IS" BASIS,
-# 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.
-
-from ._base import Config, ConfigError
-
-
-MISSING_LDAP3 = (
-    "Missing ldap3 library. This is required for LDAP Authentication."
-)
-
-
-class LDAPMode(object):
-    SIMPLE = "simple",
-    SEARCH = "search",
-
-    LIST = (SIMPLE, SEARCH)
-
-
-class LDAPConfig(Config):
-    def read_config(self, config):
-        ldap_config = config.get("ldap_config", {})
-
-        self.ldap_enabled = ldap_config.get("enabled", False)
-
-        if self.ldap_enabled:
-            # verify dependencies are available
-            try:
-                import ldap3
-                ldap3  # to stop unused lint
-            except ImportError:
-                raise ConfigError(MISSING_LDAP3)
-
-            self.ldap_mode = LDAPMode.SIMPLE
-
-            # verify config sanity
-            self.require_keys(ldap_config, [
-                "uri",
-                "base",
-                "attributes",
-            ])
-
-            self.ldap_uri = ldap_config["uri"]
-            self.ldap_start_tls = ldap_config.get("start_tls", False)
-            self.ldap_base = ldap_config["base"]
-            self.ldap_attributes = ldap_config["attributes"]
-
-            if "bind_dn" in ldap_config:
-                self.ldap_mode = LDAPMode.SEARCH
-                self.require_keys(ldap_config, [
-                    "bind_dn",
-                    "bind_password",
-                ])
-
-                self.ldap_bind_dn = ldap_config["bind_dn"]
-                self.ldap_bind_password = ldap_config["bind_password"]
-                self.ldap_filter = ldap_config.get("filter", None)
-
-            # verify attribute lookup
-            self.require_keys(ldap_config['attributes'], [
-                "uid",
-                "name",
-                "mail",
-            ])
-
-    def require_keys(self, config, required):
-        missing = [key for key in required if key not in config]
-        if missing:
-            raise ConfigError(
-                "LDAP enabled but missing required config values: {}".format(
-                    ", ".join(missing)
-                )
-            )
-
-    def default_config(self, **kwargs):
-        return """\
-        # ldap_config:
-        #   enabled: true
-        #   uri: "ldap://ldap.example.com:389"
-        #   start_tls: true
-        #   base: "ou=users,dc=example,dc=com"
-        #   attributes:
-        #      uid: "cn"
-        #      mail: "email"
-        #      name: "givenName"
-        #   #bind_dn:
-        #   #bind_password:
-        #   #filter: "(objectClass=posixAccount)"
-        """
diff --git a/synapse/config/password_auth_providers.py b/synapse/config/password_auth_providers.py
new file mode 100644
index 0000000000..f6d9bb1c62
--- /dev/null
+++ b/synapse/config/password_auth_providers.py
@@ -0,0 +1,61 @@
+# -*- coding: utf-8 -*-
+# Copyright 2016 Openmarket
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# 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.
+
+from ._base import Config
+
+import importlib
+
+
+class PasswordAuthProviderConfig(Config):
+    def read_config(self, config):
+        self.password_providers = []
+
+        # We want to be backwards compatible with the old `ldap_config`
+        # param.
+        ldap_config = config.get("ldap_config", {})
+        self.ldap_enabled = ldap_config.get("enabled", False)
+        if self.ldap_enabled:
+            from synapse.util.ldap_auth_provider import LdapAuthProvider
+            parsed_config = LdapAuthProvider.parse_config(ldap_config)
+            self.password_providers.append((LdapAuthProvider, parsed_config))
+
+        providers = config.get("password_providers", [])
+        for provider in providers:
+            # We need to import the module, and then pick the class out of
+            # that, so we split based on the last dot.
+            module, clz = provider['module'].rsplit(".", 1)
+            module = importlib.import_module(module)
+            provider_class = getattr(module, clz)
+
+            provider_config = provider_class.parse_config(provider["config"])
+            self.password_providers.append((provider_class, provider_config))
+
+    def default_config(self, **kwargs):
+        return """\
+        # password_providers:
+        #     - module: "synapse.util.ldap_auth_provider.LdapAuthProvider"
+        #       config:
+        #         enabled: true
+        #         uri: "ldap://ldap.example.com:389"
+        #         start_tls: true
+        #         base: "ou=users,dc=example,dc=com"
+        #         attributes:
+        #            uid: "cn"
+        #            mail: "email"
+        #            name: "givenName"
+        #         #bind_dn:
+        #         #bind_password:
+        #         #filter: "(objectClass=posixAccount)"
+        """
diff --git a/synapse/handlers/auth.py b/synapse/handlers/auth.py
index 6b8de1e7cf..dc0fe60e1b 100644
--- a/synapse/handlers/auth.py
+++ b/synapse/handlers/auth.py
@@ -20,7 +20,6 @@ from synapse.api.constants import LoginType
 from synapse.types import UserID
 from synapse.api.errors import AuthError, LoginError, Codes, StoreError, SynapseError
 from synapse.util.async import run_on_reactor
-from synapse.config.ldap import LDAPMode
 
 from twisted.web.client import PartialDownloadError
 
@@ -29,13 +28,6 @@ import bcrypt
 import pymacaroons
 import simplejson
 
-try:
-    import ldap3
-    import ldap3.core.exceptions
-except ImportError:
-    ldap3 = None
-    pass
-
 import synapse.util.stringutils as stringutils
 
 
@@ -60,21 +52,14 @@ class AuthHandler(BaseHandler):
         self.bcrypt_rounds = hs.config.bcrypt_rounds
         self.sessions = {}
 
-        self.ldap_enabled = hs.config.ldap_enabled
-        if self.ldap_enabled:
-            if not ldap3:
-                raise RuntimeError(
-                    'Missing ldap3 library. This is required for LDAP Authentication.'
-                )
-            self.ldap_mode = hs.config.ldap_mode
-            self.ldap_uri = hs.config.ldap_uri
-            self.ldap_start_tls = hs.config.ldap_start_tls
-            self.ldap_base = hs.config.ldap_base
-            self.ldap_attributes = hs.config.ldap_attributes
-            if self.ldap_mode == LDAPMode.SEARCH:
-                self.ldap_bind_dn = hs.config.ldap_bind_dn
-                self.ldap_bind_password = hs.config.ldap_bind_password
-                self.ldap_filter = hs.config.ldap_filter
+        account_handler = _AccountHandler(
+            hs, check_user_exists=self.check_user_exists
+        )
+
+        self.password_providers = [
+            module(config=config, account_handler=account_handler)
+            for module, config in hs.config.password_providers
+        ]
 
         self.hs = hs  # FIXME better possibility to access registrationHandler later?
         self.device_handler = hs.get_device_handler()
@@ -497,9 +482,10 @@ class AuthHandler(BaseHandler):
         Raises:
             LoginError if login fails
         """
-        valid_ldap = yield self._check_ldap_password(user_id, password)
-        if valid_ldap:
-            defer.returnValue(user_id)
+        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)
 
@@ -536,275 +522,6 @@ class AuthHandler(BaseHandler):
             defer.returnValue(None)
         defer.returnValue(user_id)
 
-    def _ldap_simple_bind(self, server, localpart, password):
-        """ Attempt a simple bind with the credentials
-            given by the user against the LDAP server.
-
-            Returns True, LDAP3Connection
-                if the bind was successful
-            Returns False, None
-                if an error occured
-        """
-
-        try:
-            # bind with the the local users ldap credentials
-            bind_dn = "{prop}={value},{base}".format(
-                prop=self.ldap_attributes['uid'],
-                value=localpart,
-                base=self.ldap_base
-            )
-            conn = ldap3.Connection(server, bind_dn, password)
-            logger.debug(
-                "Established LDAP connection in simple bind mode: %s",
-                conn
-            )
-
-            if self.ldap_start_tls:
-                conn.start_tls()
-                logger.debug(
-                    "Upgraded LDAP connection in simple bind mode through StartTLS: %s",
-                    conn
-                )
-
-            if conn.bind():
-                # GOOD: bind okay
-                logger.debug("LDAP Bind successful in simple bind mode.")
-                return True, conn
-
-            # BAD: bind failed
-            logger.info(
-                "Binding against LDAP failed for '%s' failed: %s",
-                localpart, conn.result['description']
-            )
-            conn.unbind()
-            return False, None
-
-        except ldap3.core.exceptions.LDAPException as e:
-            logger.warn("Error during LDAP authentication: %s", e)
-            return False, None
-
-    def _ldap_authenticated_search(self, server, localpart, password):
-        """ Attempt to login with the preconfigured bind_dn
-            and then continue searching and filtering within
-            the base_dn
-
-            Returns (True, LDAP3Connection)
-                if a single matching DN within the base was found
-                that matched the filter expression, and with which
-                a successful bind was achieved
-
-                The LDAP3Connection returned is the instance that was used to
-                verify the password not the one using the configured bind_dn.
-            Returns (False, None)
-                if an error occured
-        """
-
-        try:
-            conn = ldap3.Connection(
-                server,
-                self.ldap_bind_dn,
-                self.ldap_bind_password
-            )
-            logger.debug(
-                "Established LDAP connection in search mode: %s",
-                conn
-            )
-
-            if self.ldap_start_tls:
-                conn.start_tls()
-                logger.debug(
-                    "Upgraded LDAP connection in search mode through StartTLS: %s",
-                    conn
-                )
-
-            if not conn.bind():
-                logger.warn(
-                    "Binding against LDAP with `bind_dn` failed: %s",
-                    conn.result['description']
-                )
-                conn.unbind()
-                return False, None
-
-            # construct search_filter like (uid=localpart)
-            query = "({prop}={value})".format(
-                prop=self.ldap_attributes['uid'],
-                value=localpart
-            )
-            if self.ldap_filter:
-                # combine with the AND expression
-                query = "(&{query}{filter})".format(
-                    query=query,
-                    filter=self.ldap_filter
-                )
-            logger.debug(
-                "LDAP search filter: %s",
-                query
-            )
-            conn.search(
-                search_base=self.ldap_base,
-                search_filter=query
-            )
-
-            if len(conn.response) == 1:
-                # GOOD: found exactly one result
-                user_dn = conn.response[0]['dn']
-                logger.debug('LDAP search found dn: %s', user_dn)
-
-                # unbind and simple bind with user_dn to verify the password
-                # Note: do not use rebind(), for some reason it did not verify
-                #       the password for me!
-                conn.unbind()
-                return self._ldap_simple_bind(server, localpart, password)
-            else:
-                # BAD: found 0 or > 1 results, abort!
-                if len(conn.response) == 0:
-                    logger.info(
-                        "LDAP search returned no results for '%s'",
-                        localpart
-                    )
-                else:
-                    logger.info(
-                        "LDAP search returned too many (%s) results for '%s'",
-                        len(conn.response), localpart
-                    )
-                conn.unbind()
-                return False, None
-
-        except ldap3.core.exceptions.LDAPException as e:
-            logger.warn("Error during LDAP authentication: %s", e)
-            return False, None
-
-    @defer.inlineCallbacks
-    def _check_ldap_password(self, user_id, password):
-        """ Attempt to authenticate a user against an LDAP Server
-            and register an account if none exists.
-
-            Returns:
-                True if authentication against LDAP was successful
-        """
-
-        if not ldap3 or not self.ldap_enabled:
-            defer.returnValue(False)
-
-        localpart = UserID.from_string(user_id).localpart
-
-        try:
-            server = ldap3.Server(self.ldap_uri)
-            logger.debug(
-                "Attempting LDAP connection with %s",
-                self.ldap_uri
-            )
-
-            if self.ldap_mode == LDAPMode.SIMPLE:
-                result, conn = self._ldap_simple_bind(
-                    server=server, localpart=localpart, password=password
-                )
-                logger.debug(
-                    'LDAP authentication method simple bind returned: %s (conn: %s)',
-                    result,
-                    conn
-                )
-                if not result:
-                    defer.returnValue(False)
-            elif self.ldap_mode == LDAPMode.SEARCH:
-                result, conn = self._ldap_authenticated_search(
-                    server=server, localpart=localpart, password=password
-                )
-                logger.debug(
-                    'LDAP auth method authenticated search returned: %s (conn: %s)',
-                    result,
-                    conn
-                )
-                if not result:
-                    defer.returnValue(False)
-            else:
-                raise RuntimeError(
-                    'Invalid LDAP mode specified: {mode}'.format(
-                        mode=self.ldap_mode
-                    )
-                )
-
-            try:
-                logger.info(
-                    "User authenticated against LDAP server: %s",
-                    conn
-                )
-            except NameError:
-                logger.warn("Authentication method yielded no LDAP connection, aborting!")
-                defer.returnValue(False)
-
-            # check if user with user_id exists
-            if (yield self.check_user_exists(user_id)):
-                # exists, authentication complete
-                conn.unbind()
-                defer.returnValue(True)
-
-            else:
-                # does not exist, fetch metadata for account creation from
-                # existing ldap connection
-                query = "({prop}={value})".format(
-                    prop=self.ldap_attributes['uid'],
-                    value=localpart
-                )
-
-                if self.ldap_mode == LDAPMode.SEARCH and self.ldap_filter:
-                    query = "(&{filter}{user_filter})".format(
-                        filter=query,
-                        user_filter=self.ldap_filter
-                    )
-                logger.debug(
-                    "ldap registration filter: %s",
-                    query
-                )
-
-                conn.search(
-                    search_base=self.ldap_base,
-                    search_filter=query,
-                    attributes=[
-                        self.ldap_attributes['name'],
-                        self.ldap_attributes['mail']
-                    ]
-                )
-
-                if len(conn.response) == 1:
-                    attrs = conn.response[0]['attributes']
-                    mail = attrs[self.ldap_attributes['mail']][0]
-                    name = attrs[self.ldap_attributes['name']][0]
-
-                    # create account
-                    registration_handler = self.hs.get_handlers().registration_handler
-                    user_id, access_token = (
-                        yield registration_handler.register(localpart=localpart)
-                    )
-
-                    # TODO: bind email, set displayname with data from ldap directory
-
-                    logger.info(
-                        "Registration based on LDAP data was successful: %d: %s (%s, %)",
-                        user_id,
-                        localpart,
-                        name,
-                        mail
-                    )
-
-                    defer.returnValue(True)
-                else:
-                    if len(conn.response) == 0:
-                        logger.warn("LDAP registration failed, no result.")
-                    else:
-                        logger.warn(
-                            "LDAP registration failed, too many results (%s)",
-                            len(conn.response)
-                        )
-
-                    defer.returnValue(False)
-
-            defer.returnValue(False)
-
-        except ldap3.core.exceptions.LDAPException as e:
-            logger.warn("Error during ldap authentication: %s", e)
-            defer.returnValue(False)
-
     @defer.inlineCallbacks
     def issue_access_token(self, user_id, device_id=None):
         access_token = self.generate_access_token(user_id)
@@ -942,3 +659,30 @@ class AuthHandler(BaseHandler):
                                  stored_hash.encode('utf-8')) == stored_hash
         else:
             return False
+
+
+class _AccountHandler(object):
+    """A proxy object that gets passed to password auth providers so they
+    can register new users etc if necessary.
+    """
+    def __init__(self, hs, check_user_exists):
+        self.hs = hs
+
+        self._check_user_exists = check_user_exists
+
+    def check_user_exists(self, user_id):
+        """Check if user exissts.
+
+        Returns:
+            Deferred(bool)
+        """
+        return self._check_user_exists(user_id)
+
+    def register(self, localpart):
+        """Registers a new user with given localpart
+
+        Returns:
+            Deferred: a 2-tuple of (user_id, access_token)
+        """
+        reg = self.hs.get_handlers().registration_handler
+        return reg.register(localpart=localpart)
diff --git a/synapse/util/ldap_auth_provider.py b/synapse/util/ldap_auth_provider.py
new file mode 100644
index 0000000000..f852e9b037
--- /dev/null
+++ b/synapse/util/ldap_auth_provider.py
@@ -0,0 +1,368 @@
+
+from twisted.internet import defer
+
+from synapse.config._base import ConfigError
+from synapse.types import UserID
+
+import ldap3
+import ldap3.core.exceptions
+
+import logging
+
+try:
+    import ldap3
+    import ldap3.core.exceptions
+except ImportError:
+    ldap3 = None
+    pass
+
+
+logger = logging.getLogger(__name__)
+
+
+class LDAPMode(object):
+    SIMPLE = "simple",
+    SEARCH = "search",
+
+    LIST = (SIMPLE, SEARCH)
+
+
+class LdapAuthProvider(object):
+    __version__ = "0.1"
+
+    def __init__(self, config, account_handler):
+        self.account_handler = account_handler
+
+        if not ldap3:
+            raise RuntimeError(
+                'Missing ldap3 library. This is required for LDAP Authentication.'
+            )
+
+        self.ldap_mode = config.mode
+        self.ldap_uri = config.uri
+        self.ldap_start_tls = config.start_tls
+        self.ldap_base = config.base
+        self.ldap_attributes = config.attributes
+        if self.ldap_mode == LDAPMode.SEARCH:
+            self.ldap_bind_dn = config.bind_dn
+            self.ldap_bind_password = config.bind_password
+            self.ldap_filter = config.filter
+
+    @defer.inlineCallbacks
+    def check_password(self, user_id, password):
+        """ Attempt to authenticate a user against an LDAP Server
+            and register an account if none exists.
+
+            Returns:
+                True if authentication against LDAP was successful
+        """
+        localpart = UserID.from_string(user_id).localpart
+
+        try:
+            server = ldap3.Server(self.ldap_uri)
+            logger.debug(
+                "Attempting LDAP connection with %s",
+                self.ldap_uri
+            )
+
+            if self.ldap_mode == LDAPMode.SIMPLE:
+                result, conn = self._ldap_simple_bind(
+                    server=server, localpart=localpart, password=password
+                )
+                logger.debug(
+                    'LDAP authentication method simple bind returned: %s (conn: %s)',
+                    result,
+                    conn
+                )
+                if not result:
+                    defer.returnValue(False)
+            elif self.ldap_mode == LDAPMode.SEARCH:
+                result, conn = self._ldap_authenticated_search(
+                    server=server, localpart=localpart, password=password
+                )
+                logger.debug(
+                    'LDAP auth method authenticated search returned: %s (conn: %s)',
+                    result,
+                    conn
+                )
+                if not result:
+                    defer.returnValue(False)
+            else:
+                raise RuntimeError(
+                    'Invalid LDAP mode specified: {mode}'.format(
+                        mode=self.ldap_mode
+                    )
+                )
+
+            try:
+                logger.info(
+                    "User authenticated against LDAP server: %s",
+                    conn
+                )
+            except NameError:
+                logger.warn(
+                    "Authentication method yielded no LDAP connection, aborting!"
+                )
+                defer.returnValue(False)
+
+            # check if user with user_id exists
+            if (yield self.account_handler.check_user_exists(user_id)):
+                # exists, authentication complete
+                conn.unbind()
+                defer.returnValue(True)
+
+            else:
+                # does not exist, fetch metadata for account creation from
+                # existing ldap connection
+                query = "({prop}={value})".format(
+                    prop=self.ldap_attributes['uid'],
+                    value=localpart
+                )
+
+                if self.ldap_mode == LDAPMode.SEARCH and self.ldap_filter:
+                    query = "(&{filter}{user_filter})".format(
+                        filter=query,
+                        user_filter=self.ldap_filter
+                    )
+                logger.debug(
+                    "ldap registration filter: %s",
+                    query
+                )
+
+                conn.search(
+                    search_base=self.ldap_base,
+                    search_filter=query,
+                    attributes=[
+                        self.ldap_attributes['name'],
+                        self.ldap_attributes['mail']
+                    ]
+                )
+
+                if len(conn.response) == 1:
+                    attrs = conn.response[0]['attributes']
+                    mail = attrs[self.ldap_attributes['mail']][0]
+                    name = attrs[self.ldap_attributes['name']][0]
+
+                    # create account
+                    user_id, access_token = (
+                        yield self.account_handler.register(localpart=localpart)
+                    )
+
+                    # TODO: bind email, set displayname with data from ldap directory
+
+                    logger.info(
+                        "Registration based on LDAP data was successful: %d: %s (%s, %)",
+                        user_id,
+                        localpart,
+                        name,
+                        mail
+                    )
+
+                    defer.returnValue(True)
+                else:
+                    if len(conn.response) == 0:
+                        logger.warn("LDAP registration failed, no result.")
+                    else:
+                        logger.warn(
+                            "LDAP registration failed, too many results (%s)",
+                            len(conn.response)
+                        )
+
+                    defer.returnValue(False)
+
+            defer.returnValue(False)
+
+        except ldap3.core.exceptions.LDAPException as e:
+            logger.warn("Error during ldap authentication: %s", e)
+            defer.returnValue(False)
+
+    @staticmethod
+    def parse_config(config):
+        class _LdapConfig(object):
+            pass
+
+        ldap_config = _LdapConfig()
+
+        ldap_config.enabled = config.get("enabled", False)
+
+        ldap_config.mode = LDAPMode.SIMPLE
+
+        # verify config sanity
+        _require_keys(config, [
+            "uri",
+            "base",
+            "attributes",
+        ])
+
+        ldap_config.uri = config["uri"]
+        ldap_config.start_tls = config.get("start_tls", False)
+        ldap_config.base = config["base"]
+        ldap_config.attributes = config["attributes"]
+
+        if "bind_dn" in config:
+            ldap_config.mode = LDAPMode.SEARCH
+            _require_keys(config, [
+                "bind_dn",
+                "bind_password",
+            ])
+
+            ldap_config.bind_dn = config["bind_dn"]
+            ldap_config.bind_password = config["bind_password"]
+            ldap_config.filter = config.get("filter", None)
+
+        # verify attribute lookup
+        _require_keys(config['attributes'], [
+            "uid",
+            "name",
+            "mail",
+        ])
+
+        return ldap_config
+
+    def _ldap_simple_bind(self, server, localpart, password):
+        """ Attempt a simple bind with the credentials
+            given by the user against the LDAP server.
+
+            Returns True, LDAP3Connection
+                if the bind was successful
+            Returns False, None
+                if an error occured
+        """
+
+        try:
+            # bind with the the local users ldap credentials
+            bind_dn = "{prop}={value},{base}".format(
+                prop=self.ldap_attributes['uid'],
+                value=localpart,
+                base=self.ldap_base
+            )
+            conn = ldap3.Connection(server, bind_dn, password)
+            logger.debug(
+                "Established LDAP connection in simple bind mode: %s",
+                conn
+            )
+
+            if self.ldap_start_tls:
+                conn.start_tls()
+                logger.debug(
+                    "Upgraded LDAP connection in simple bind mode through StartTLS: %s",
+                    conn
+                )
+
+            if conn.bind():
+                # GOOD: bind okay
+                logger.debug("LDAP Bind successful in simple bind mode.")
+                return True, conn
+
+            # BAD: bind failed
+            logger.info(
+                "Binding against LDAP failed for '%s' failed: %s",
+                localpart, conn.result['description']
+            )
+            conn.unbind()
+            return False, None
+
+        except ldap3.core.exceptions.LDAPException as e:
+            logger.warn("Error during LDAP authentication: %s", e)
+            return False, None
+
+    def _ldap_authenticated_search(self, server, localpart, password):
+        """ Attempt to login with the preconfigured bind_dn
+            and then continue searching and filtering within
+            the base_dn
+
+            Returns (True, LDAP3Connection)
+                if a single matching DN within the base was found
+                that matched the filter expression, and with which
+                a successful bind was achieved
+
+                The LDAP3Connection returned is the instance that was used to
+                verify the password not the one using the configured bind_dn.
+            Returns (False, None)
+                if an error occured
+        """
+
+        try:
+            conn = ldap3.Connection(
+                server,
+                self.ldap_bind_dn,
+                self.ldap_bind_password
+            )
+            logger.debug(
+                "Established LDAP connection in search mode: %s",
+                conn
+            )
+
+            if self.ldap_start_tls:
+                conn.start_tls()
+                logger.debug(
+                    "Upgraded LDAP connection in search mode through StartTLS: %s",
+                    conn
+                )
+
+            if not conn.bind():
+                logger.warn(
+                    "Binding against LDAP with `bind_dn` failed: %s",
+                    conn.result['description']
+                )
+                conn.unbind()
+                return False, None
+
+            # construct search_filter like (uid=localpart)
+            query = "({prop}={value})".format(
+                prop=self.ldap_attributes['uid'],
+                value=localpart
+            )
+            if self.ldap_filter:
+                # combine with the AND expression
+                query = "(&{query}{filter})".format(
+                    query=query,
+                    filter=self.ldap_filter
+                )
+            logger.debug(
+                "LDAP search filter: %s",
+                query
+            )
+            conn.search(
+                search_base=self.ldap_base,
+                search_filter=query
+            )
+
+            if len(conn.response) == 1:
+                # GOOD: found exactly one result
+                user_dn = conn.response[0]['dn']
+                logger.debug('LDAP search found dn: %s', user_dn)
+
+                # unbind and simple bind with user_dn to verify the password
+                # Note: do not use rebind(), for some reason it did not verify
+                #       the password for me!
+                conn.unbind()
+                return self._ldap_simple_bind(server, localpart, password)
+            else:
+                # BAD: found 0 or > 1 results, abort!
+                if len(conn.response) == 0:
+                    logger.info(
+                        "LDAP search returned no results for '%s'",
+                        localpart
+                    )
+                else:
+                    logger.info(
+                        "LDAP search returned too many (%s) results for '%s'",
+                        len(conn.response), localpart
+                    )
+                conn.unbind()
+                return False, None
+
+        except ldap3.core.exceptions.LDAPException as e:
+            logger.warn("Error during LDAP authentication: %s", e)
+            return False, None
+
+
+def _require_keys(config, required):
+    missing = [key for key in required if key not in config]
+    if missing:
+        raise ConfigError(
+            "LDAP enabled but missing required config values: {}".format(
+                ", ".join(missing)
+            )
+        )