Enhancements to OIDC configuration handling

changelog.d/9105.feature

@@ -0,0 +1 @@
+Add support for multiple SSO Identity Providers.

synapse/config/oidc_config.py

@@ -1,5 +1,6 @@
 # -*- coding: utf-8 -*-
 # Copyright 2020 Quentin Gliech
+# Copyright 2020 The Matrix.org Foundation C.I.C.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -13,7 +14,13 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from typing import Optional, Type
+
+import attr
+
+from synapse.config._util import validate_config
 from synapse.python_dependencies import DependencyException, check_requirements
+from synapse.types import Collection, JsonDict
 from synapse.util.module_loader import load_module
 
 from ._base import Config, ConfigError
@@ -25,65 +32,32 @@ class OIDCConfig(Config):
     section = "oidc"
 
     def read_config(self, config, **kwargs):
-        self.oidc_enabled = False
+        validate_config(MAIN_CONFIG_SCHEMA, config, ())
+
+        self.oidc_provider = None  # type: Optional[OidcProviderConfig]
 
         oidc_config = config.get("oidc_config")
+        if oidc_config and oidc_config.get("enabled", False):
+            validate_config(OIDC_PROVIDER_CONFIG_SCHEMA, oidc_config, "oidc_config")
+            self.oidc_provider = _parse_oidc_config_dict(oidc_config)
 
-        if not oidc_config or not oidc_config.get("enabled", False):
+        if not self.oidc_provider:
             return
 
         try:
             check_requirements("oidc")
         except DependencyException as e:
-            raise ConfigError(e.message)
+            raise ConfigError(e.message) from e
 
         public_baseurl = self.public_baseurl
         if public_baseurl is None:
             raise ConfigError("oidc_config requires a public_baseurl to be set")
         self.oidc_callback_url = public_baseurl + "_synapse/oidc/callback"
 
-        self.oidc_enabled = True
-        self.oidc_discover = oidc_config.get("discover", True)
-        self.oidc_issuer = oidc_config["issuer"]
-        self.oidc_client_id = oidc_config["client_id"]
-        self.oidc_client_secret = oidc_config["client_secret"]
-        self.oidc_client_auth_method = oidc_config.get(
-            "client_auth_method", "client_secret_basic"
-        )
-        self.oidc_scopes = oidc_config.get("scopes", ["openid"])
-        self.oidc_authorization_endpoint = oidc_config.get("authorization_endpoint")
-        self.oidc_token_endpoint = oidc_config.get("token_endpoint")
-        self.oidc_userinfo_endpoint = oidc_config.get("userinfo_endpoint")
-        self.oidc_jwks_uri = oidc_config.get("jwks_uri")
-        self.oidc_skip_verification = oidc_config.get("skip_verification", False)
-        self.oidc_user_profile_method = oidc_config.get("user_profile_method", "auto")
-        self.oidc_allow_existing_users = oidc_config.get("allow_existing_users", False)
-
-        ump_config = oidc_config.get("user_mapping_provider", {})
-        ump_config.setdefault("module", DEFAULT_USER_MAPPING_PROVIDER)
-        ump_config.setdefault("config", {})
-
-        (
-            self.oidc_user_mapping_provider_class,
-            self.oidc_user_mapping_provider_config,
-        ) = load_module(ump_config, ("oidc_config", "user_mapping_provider"))
-
-        # Ensure loaded user mapping module has defined all necessary methods
-        required_methods = [
-            "get_remote_user_id",
-            "map_user_attributes",
-        ]
-        missing_methods = [
-            method
-            for method in required_methods
-            if not hasattr(self.oidc_user_mapping_provider_class, method)
-        ]
-        if missing_methods:
-            raise ConfigError(
-                "Class specified by oidc_config."
-                "user_mapping_provider.module is missing required "
-                "methods: %s" % (", ".join(missing_methods),)
-            )
+    @property
+    def oidc_enabled(self) -> bool:
+        # OIDC is enabled if we have a provider
+        return bool(self.oidc_provider)
 
     def generate_config_section(self, config_dir_path, server_name, **kwargs):
         return """\
@@ -224,3 +198,154 @@ def generate_config_section(self, config_dir_path, server_name, **kwargs):
         """.format(
             mapping_provider=DEFAULT_USER_MAPPING_PROVIDER
         )
+
+
+# jsonschema definition of the configuration settings for an oidc identity provider
+OIDC_PROVIDER_CONFIG_SCHEMA = {
+    "type": "object",
+    "required": ["issuer", "client_id", "client_secret"],
+    "properties": {
+        "discover": {"type": "boolean"},
+        "issuer": {"type": "string"},
+        "client_id": {"type": "string"},
+        "client_secret": {"type": "string"},
+        "client_auth_method": {
+            "type": "string",
+            # the following list is the same as the keys of
+            # authlib.oauth2.auth.ClientAuth.DEFAULT_AUTH_METHODS. We inline it
+            # to avoid importing authlib here.
+            "enum": ["client_secret_basic", "client_secret_post", "none"],
+        },
+        "scopes": {"type": "array", "items": {"type": "string"}},
+        "authorization_endpoint": {"type": "string"},
+        "token_endpoint": {"type": "string"},
+        "userinfo_endpoint": {"type": "string"},
+        "jwks_uri": {"type": "string"},
+        "skip_verification": {"type": "boolean"},
+        "user_profile_method": {
+            "type": "string",
+            "enum": ["auto", "userinfo_endpoint"],
+        },
+        "allow_existing_users": {"type": "boolean"},
+        "user_mapping_provider": {"type": ["object", "null"]},
+    },
+}
+
+# the `oidc_config` setting can either be None (as it is in the default
+# config), or an object. If an object, it is ignored unless it has an "enabled: True"
+# property.
+#
+# It's *possible* to represent this with jsonschema, but the resultant errors aren't
+# particularly clear, so we just check for either an object or a null here, and do
+# additional checks in the code.
+OIDC_CONFIG_SCHEMA = {"oneOf": [{"type": "null"}, {"type": "object"}]}
+
+MAIN_CONFIG_SCHEMA = {
+    "type": "object",
+    "properties": {"oidc_config": OIDC_CONFIG_SCHEMA},
+}
+
+
+def _parse_oidc_config_dict(oidc_config: JsonDict) -> "OidcProviderConfig":
+    """Take the configuration dict and parse it into an OidcProviderConfig
+
+    Raises:
+        ConfigError if the configuration is malformed.
+    """
+    ump_config = oidc_config.get("user_mapping_provider", {})
+    ump_config.setdefault("module", DEFAULT_USER_MAPPING_PROVIDER)
+    ump_config.setdefault("config", {})
+
+    (user_mapping_provider_class, user_mapping_provider_config,) = load_module(
+        ump_config, ("oidc_config", "user_mapping_provider")
+    )
+
+    # Ensure loaded user mapping module has defined all necessary methods
+    required_methods = [
+        "get_remote_user_id",
+        "map_user_attributes",
+    ]
+    missing_methods = [
+        method
+        for method in required_methods
+        if not hasattr(user_mapping_provider_class, method)
+    ]
+    if missing_methods:
+        raise ConfigError(
+            "Class specified by oidc_config."
+            "user_mapping_provider.module is missing required "
+            "methods: %s" % (", ".join(missing_methods),)
+        )
+
+    return OidcProviderConfig(
+        discover=oidc_config.get("discover", True),
+        issuer=oidc_config["issuer"],
+        client_id=oidc_config["client_id"],
+        client_secret=oidc_config["client_secret"],
+        client_auth_method=oidc_config.get("client_auth_method", "client_secret_basic"),
+        scopes=oidc_config.get("scopes", ["openid"]),
+        authorization_endpoint=oidc_config.get("authorization_endpoint"),
+        token_endpoint=oidc_config.get("token_endpoint"),
+        userinfo_endpoint=oidc_config.get("userinfo_endpoint"),
+        jwks_uri=oidc_config.get("jwks_uri"),
+        skip_verification=oidc_config.get("skip_verification", False),
+        user_profile_method=oidc_config.get("user_profile_method", "auto"),
+        allow_existing_users=oidc_config.get("allow_existing_users", False),
+        user_mapping_provider_class=user_mapping_provider_class,
+        user_mapping_provider_config=user_mapping_provider_config,
+    )
+
+
+@attr.s
+class OidcProviderConfig:
+    # whether the OIDC discovery mechanism is used to discover endpoints
+    discover = attr.ib(type=bool)
+
+    # the OIDC issuer. Used to validate tokens and (if discovery is enabled) to
+    # discover the provider's endpoints.
+    issuer = attr.ib(type=str)
+
+    # oauth2 client id to use
+    client_id = attr.ib(type=str)
+
+    # oauth2 client secret to use
+    client_secret = attr.ib(type=str)
+
+    # auth method to use when exchanging the token.
+    # Valid values are 'client_secret_basic', 'client_secret_post' and
+    # 'none'.
+    client_auth_method = attr.ib(type=str)
+
+    # list of scopes to request
+    scopes = attr.ib(type=Collection[str])
+
+    # the oauth2 authorization endpoint. Required if discovery is disabled.
+    authorization_endpoint = attr.ib(type=Optional[str])
+
+    # the oauth2 token endpoint. Required if discovery is disabled.
+    token_endpoint = attr.ib(type=Optional[str])
+
+    # the OIDC userinfo endpoint. Required if discovery is disabled and the
+    # "openid" scope is not requested.
+    userinfo_endpoint = attr.ib(type=Optional[str])
+
+    # URI where to fetch the JWKS. Required if discovery is disabled and the
+    # "openid" scope is used.
+    jwks_uri = attr.ib(type=Optional[str])
+
+    # Whether to skip metadata verification
+    skip_verification = attr.ib(type=bool)
+
+    # Whether to fetch the user profile from the userinfo endpoint. Valid
+    # values are: "auto" or "userinfo_endpoint".
+    user_profile_method = attr.ib(type=str)
+
+    # whether to allow a user logging in via OIDC to match a pre-existing account
+    # instead of failing
+    allow_existing_users = attr.ib(type=bool)
+
+    # the class of the user mapping provider
+    user_mapping_provider_class = attr.ib(type=Type)
+
+    # the config of the user mapping provider
+    user_mapping_provider_config = attr.ib()

synapse/handlers/oidc_handler.py

@@ -94,27 +94,30 @@ def __init__(self, hs: "HomeServer"):
         self._token_generator = OidcSessionTokenGenerator(hs)
 
         self._callback_url = hs.config.oidc_callback_url  # type: str
-        self._scopes = hs.config.oidc_scopes  # type: List[str]
-        self._user_profile_method = hs.config.oidc_user_profile_method  # type: str
+
+        provider = hs.config.oidc.oidc_provider
+        # we should not have been instantiated if there is no configured provider.
+        assert provider is not None
+
+        self._scopes = provider.scopes
+        self._user_profile_method = provider.user_profile_method
         self._client_auth = ClientAuth(
-            hs.config.oidc_client_id,
-            hs.config.oidc_client_secret,
-            hs.config.oidc_client_auth_method,
+            provider.client_id, provider.client_secret, provider.client_auth_method,
         )  # type: ClientAuth
-        self._client_auth_method = hs.config.oidc_client_auth_method  # type: str
+        self._client_auth_method = provider.client_auth_method
         self._provider_metadata = OpenIDProviderMetadata(
-            issuer=hs.config.oidc_issuer,
-            authorization_endpoint=hs.config.oidc_authorization_endpoint,
-            token_endpoint=hs.config.oidc_token_endpoint,
-            userinfo_endpoint=hs.config.oidc_userinfo_endpoint,
-            jwks_uri=hs.config.oidc_jwks_uri,
+            issuer=provider.issuer,
+            authorization_endpoint=provider.authorization_endpoint,
+            token_endpoint=provider.token_endpoint,
+            userinfo_endpoint=provider.userinfo_endpoint,
+            jwks_uri=provider.jwks_uri,
         )  # type: OpenIDProviderMetadata
-        self._provider_needs_discovery = hs.config.oidc_discover  # type: bool
-        self._user_mapping_provider = hs.config.oidc_user_mapping_provider_class(
-            hs.config.oidc_user_mapping_provider_config
-        )  # type: OidcMappingProvider
-        self._skip_verification = hs.config.oidc_skip_verification  # type: bool
-        self._allow_existing_users = hs.config.oidc_allow_existing_users  # type: bool
+        self._provider_needs_discovery = provider.discover
+        self._user_mapping_provider = provider.user_mapping_provider_class(
+            provider.user_mapping_provider_config
+        )
+        self._skip_verification = provider.skip_verification
+        self._allow_existing_users = provider.allow_existing_users
 
         self._http_client = hs.get_proxied_http_client()
         self._server_name = hs.config.server_name  # type: str