# Source code for aiohttp_security.abc

    import abc
    from enum import Enum
    from typing import Any, Optional, Union

    from aiohttp import web

    # see http://plope.com/pyramid_auth_design_api_postmortem

    class AbstractIdentityPolicy(metaclass=abc.ABCMeta):

        @abc.abstractmethod
        async def identify(self, request: web.Request) -> Optional[str]:
            """Return the claimed identity of the user associated request or
            ``None`` if no identity can be found associated with the request."""
            pass

        @abc.abstractmethod
        async def remember(self, request: web.Request,  # type: ignore[misc]
                           response: web.StreamResponse, identity: str, **kwargs: Any) -> None:
            """Remember identity.

            Modify response object by filling it's headers with remembered user.

            An individual identity policy and its consumers can decide on
            the composition and meaning of **kwargs.
            """
            pass

        @abc.abstractmethod
        async def forget(self, request: web.Request, response: web.StreamResponse) -> None:
            """ Modify response which can be used to 'forget' the
            current identity on subsequent requests."""
            pass

    class AbstractAuthorizationPolicy(metaclass=abc.ABCMeta):

        @abc.abstractmethod
        async def permits(self, identity: Optional[str],  # type: ignore[misc]
                          permission: Union[str, Enum], context: Any = None) -> bool:
            """Check user permissions.

            Return True if the identity is allowed the permission in the
            current context, else return False.
            """
            pass

        @abc.abstractmethod
        async def authorized_userid(self, identity: str) -> Optional[str]:
            """Retrieve authorized user id.

            Return the user_id of the user identified by the identity
            or 'None' if no user exists related to the identity.
            """
            pass