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/sources/bearer.py

@@ -0,0 +1,120 @@
+"""Bearer token authentication source."""
+
+import inspect
+import secrets
+from typing import Annotated, Any, Callable
+
+from fastapi import Depends, Request
+from fastapi.security import HTTPAuthorizationCredentials, HTTPBearer, SecurityScopes
+
+from fastapi_toolsets.exceptions import UnauthorizedError
+
+from ..abc import AuthSource, _ensure_async
+
+
+class BearerTokenAuth(AuthSource):
+    """Bearer token authentication source.
+
+    Wraps :class:`fastapi.security.HTTPBearer` for OpenAPI documentation.
+    The validator is called as ``await validator(credential, **kwargs)``
+    where ``kwargs`` are the extra keyword arguments provided at instantiation.
+
+    Args:
+        validator: Sync or async callable that receives the credential and any
+            extra keyword arguments, and returns the authenticated identity
+            (e.g. a ``User`` model). Should raise
+            :class:`~fastapi_toolsets.exceptions.UnauthorizedError` on failure.
+        prefix: Optional token prefix (e.g. ``"user_"``). If set, only tokens
+            whose value starts with this prefix are matched. The prefix is
+            **kept** in the value passed to the validator — store and compare
+            tokens with their prefix included. Use :meth:`generate_token` to
+            create correctly-prefixed tokens. This enables multiple
+            ``BearerTokenAuth`` instances in the same app (e.g. ``"user_"``
+            for user tokens, ``"org_"`` for org tokens).
+        **kwargs: Extra keyword arguments forwarded to the validator on every
+            call (e.g. ``role=Role.ADMIN``).
+    """
+
+    def __init__(
+        self,
+        validator: Callable[..., Any],
+        *,
+        prefix: str | None = None,
+        **kwargs: Any,
+    ) -> None:
+        self._validator = _ensure_async(validator)
+        self._prefix = prefix
+        self._kwargs = kwargs
+        self._scheme = HTTPBearer(auto_error=False)
+
+        async def _call(
+            security_scopes: SecurityScopes,  # noqa: ARG001
+            credentials: Annotated[
+                HTTPAuthorizationCredentials | None, Depends(self._scheme)
+            ] = None,
+        ) -> Any:
+            if credentials is None:
+                raise UnauthorizedError()
+            return await self._validate(credentials.credentials)
+
+        self._call_fn = _call
+        self.__signature__ = inspect.signature(_call)
+
+    async def _validate(self, token: str) -> Any:
+        """Check prefix and call the validator."""
+        if self._prefix is not None and not token.startswith(self._prefix):
+            raise UnauthorizedError()
+        return await self._validator(token, **self._kwargs)
+
+    async def extract(self, request: Request) -> str | None:
+        """Extract the raw credential from the request without validating.
+
+        Returns ``None`` if no ``Authorization: Bearer`` header is present,
+        the token is empty, or the token does not match the configured prefix.
+        The prefix is included in the returned value.
+        """
+        auth = request.headers.get("Authorization", "")
+        if not auth.startswith("Bearer "):
+            return None
+        token = auth[7:]
+        if not token:
+            return None
+        if self._prefix is not None and not token.startswith(self._prefix):
+            return None
+        return token
+
+    async def authenticate(self, credential: str) -> Any:
+        """Validate a credential and return the identity.
+
+        Calls ``await validator(credential, **kwargs)`` where ``kwargs`` are
+        the extra keyword arguments provided at instantiation.
+        """
+        return await self._validate(credential)
+
+    def require(self, **kwargs: Any) -> "BearerTokenAuth":
+        """Return a new instance with additional (or overriding) validator kwargs."""
+        return BearerTokenAuth(
+            self._validator,
+            prefix=self._prefix,
+            **{**self._kwargs, **kwargs},
+        )
+
+    def generate_token(self, nbytes: int = 32) -> str:
+        """Generate a secure random token for this auth source.
+
+        Returns a URL-safe random token. If a prefix is configured it is
+        prepended — the returned value is what you store in your database
+        and return to the client as-is.
+
+        Args:
+            nbytes: Number of random bytes before base64 encoding. The
+                resulting string is ``ceil(nbytes * 4 / 3)`` characters
+                (43 chars for the default 32 bytes). Defaults to 32.
+
+        Returns:
+            A ready-to-use token string (e.g. ``"user_Xk3..."``).
+        """
+        token = secrets.token_urlsafe(nbytes)
+        if self._prefix is not None:
+            return f"{self._prefix}{token}"
+        return token