Implement pluggable password auth

Allows delegating the password auth to an external module. This also
moves the LDAP auth to using this system, allowing it to be removed from
the synapse tree entirely in the future.

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)"
+        """