feat: add TOML config file support with client registrations

src/porchlight/config.py

@@ -1,7 +1,10 @@
 # src/porchlight/config.py
+import os
 from enum import StrEnum
+from typing import Any
 
-from pydantic_settings import BaseSettings
+from pydantic import BaseModel
+from pydantic_settings import BaseSettings, PydanticBaseSettingsSource, TomlConfigSettingsSource
 
 
 class StorageBackend(StrEnum):
@@ -9,8 +12,21 @@ class StorageBackend(StrEnum):
     MONGODB = "mongodb"
 
 
+class ClientConfig(BaseModel):
+    client_secret: str
+    redirect_uris: list[str]
+    response_types: list[str] = ["code"]
+    scope: list[str] = ["openid"]
+    token_endpoint_auth_method: str = "client_secret_basic"
+
+
 class Settings(BaseSettings):
-    model_config = {"env_prefix": "OIDC_OP_"}
+    model_config = {"env_prefix": "OIDC_OP_", "toml_file": "porchlight.toml"}
+
+    # Class-level bridge to pass _toml_file into the classmethod
+    # settings_customise_sources. Not thread-safe, but Settings is
+    # only instantiated once at startup.
+    _toml_file_override: str | None = None
 
     # Core
     issuer: str
@@ -40,3 +56,33 @@ class Settings(BaseSettings):
 
     # Theme
     theme: str = "default"
+
+    # OIDC clients
+    clients: dict[str, ClientConfig] = {}
+
+    def __init__(self, _toml_file: str | None = None, **kwargs: Any) -> None:
+        Settings._toml_file_override = _toml_file
+        try:
+            super().__init__(**kwargs)
+        finally:
+            Settings._toml_file_override = None
+
+    @classmethod
+    def settings_customise_sources(
+        cls,
+        settings_cls: type[BaseSettings],
+        init_settings: PydanticBaseSettingsSource,
+        env_settings: PydanticBaseSettingsSource,
+        dotenv_settings: PydanticBaseSettingsSource,
+        file_secret_settings: PydanticBaseSettingsSource,
+    ) -> tuple[PydanticBaseSettingsSource, ...]:
+        toml_file = (
+            cls._toml_file_override
+            or os.environ.get("OIDC_OP_CONFIG_FILE")
+            or settings_cls.model_config.get("toml_file")
+        )
+        return (
+            env_settings,
+            TomlConfigSettingsSource(settings_cls, toml_file=toml_file),
+            init_settings,
+        )