feat: add security module (#111)

* feat: add security module

* feat(security): add oauth helpers

* docs: add authentication example

* fix: cleanup + simplify

* docs: update module and reference

* fix: multiple security bugs + remove example for now

* feat: use async_lru for caching

* fix: rename nonce by state_token

src/fastapi_toolsets/security/abc.py

@@ -0,0 +1,55 @@
+"""Abstract base class for authentication sources."""
+
+import functools
+import inspect
+from abc import ABC, abstractmethod
+from typing import Any, Callable
+
+from fastapi import Request
+from fastapi.security import SecurityScopes
+
+from fastapi_toolsets.exceptions import UnauthorizedError
+
+
+def _ensure_async(fn: Callable[..., Any]) -> Callable[..., Any]:
+    """Wrap *fn* so it can always be awaited, caching the coroutine check at init time."""
+    if inspect.iscoroutinefunction(fn):
+        return fn
+
+    @functools.wraps(fn)
+    async def wrapper(*args: Any, **kwargs: Any) -> Any:
+        return fn(*args, **kwargs)
+
+    return wrapper
+
+
+class AuthSource(ABC):
+    """Abstract base class for authentication sources."""
+
+    def __init__(self) -> None:
+        """Set up the default FastAPI dependency signature."""
+        source = self
+
+        async def _call(
+            request: Request,
+            security_scopes: SecurityScopes,  # noqa: ARG001
+        ) -> Any:
+            credential = await source.extract(request)
+            if credential is None:
+                raise UnauthorizedError()
+            return await source.authenticate(credential)
+
+        self._call_fn: Callable[..., Any] = _call
+        self.__signature__ = inspect.signature(_call)
+
+    @abstractmethod
+    async def extract(self, request: Request) -> str | None:
+        """Extract the raw credential from the request without validating."""
+
+    @abstractmethod
+    async def authenticate(self, credential: str) -> Any:
+        """Validate a credential and return the authenticated identity."""
+
+    async def __call__(self, **kwargs: Any) -> Any:
+        """FastAPI dependency dispatch."""
+        return await self._call_fn(**kwargs)