# Source code for aiohttp_security.api

    import enum
    from typing import Any, Optional, Union

    from aiohttp import web

    from aiohttp_security.abc import AbstractAuthorizationPolicy, AbstractIdentityPolicy

    IDENTITY_KEY = web.AppKey("IDENTITY_KEY", AbstractIdentityPolicy)
    AUTZ_KEY = web.AppKey("AUTZ_KEY", AbstractAuthorizationPolicy)

    # _AIP/_AAP are shorthand for Optional[policy] when we retrieve from request.
    _AAP = Optional[AbstractAuthorizationPolicy]
    _AIP = Optional[AbstractIdentityPolicy]

    async def remember(request: web.Request, response: web.StreamResponse,
                       identity: str, **kwargs: Any) -> None:
        """Remember identity into response.

        The action is performed by identity_policy.remember()

        Usually the identity is stored in user cookies somehow but may be
        pushed into custom header also.
        """
        if not identity or not isinstance(identity, str):
            raise ValueError("Identity should be a str value.")
        identity_policy = request.config_dict.get(IDENTITY_KEY)
        if identity_policy is None:
            text = ("Security subsystem is not initialized, "
                    "call aiohttp_security.setup(...) first")
            # in order to see meaningful exception message both: on console
            # output and rendered page we add same message to *reason* and
            # *text* arguments.
            raise web.HTTPInternalServerError(reason=text, text=text)
        await identity_policy.remember(request, response, identity, **kwargs)

    async def forget(request: web.Request, response: web.StreamResponse) -> None:
        """Forget previously remembered identity.

        Usually it clears cookie or server-side storage to forget user
        session.
        """
        identity_policy = request.config_dict.get(IDENTITY_KEY)
        if identity_policy is None:
            text = ("Security subsystem is not initialized, "
                    "call aiohttp_security.setup(...) first")
            # in order to see meaningful exception message both: on console
            # output and rendered page we add same message to *reason* and
            # *text* arguments.
            raise web.HTTPInternalServerError(reason=text, text=text)
        await identity_policy.forget(request, response)

    async def authorized_userid(request: web.Request) -> Optional[str]:
        identity_policy: _AIP = request.config_dict.get(IDENTITY_KEY)
        autz_policy: _AAP = request.config_dict.get(AUTZ_KEY)
        if identity_policy is None or autz_policy is None:
            return None
        identity = await identity_policy.identify(request)
        if identity is None:
            return None  # non-registered user has None user_id
        user_id = await autz_policy.authorized_userid(identity)
        return user_id

    async def permits(request: web.Request, permission: Union[str, enum.Enum],
                      context: Any = None) -> bool:
        if not permission or not isinstance(permission, (str, enum.Enum)):
            raise ValueError("Permission should be a str or enum value.")
        identity_policy: _AIP = request.config_dict.get(IDENTITY_KEY)
        autz_policy: _AAP = request.config_dict.get(AUTZ_KEY)
        if identity_policy is None or autz_policy is None:
            return True
        identity = await identity_policy.identify(request)
        # non-registered user still may have some permissions
        access = await autz_policy.permits(identity, permission, context)
        return access

    async def is_anonymous(request: web.Request) -> bool:
        """Check if user is anonymous.

        User is considered anonymous if there is not identity
        in request.
        """
        identity_policy = request.config_dict.get(IDENTITY_KEY)
        if identity_policy is None:
            return True
        identity = await identity_policy.identify(request)
        if identity is None:
            return True
        return False

    async def check_authorized(request: web.Request) -> str:
        """Checker that raises HTTPUnauthorized for anonymous users.
        """
        userid = await authorized_userid(request)
        if userid is None:
            raise web.HTTPUnauthorized()
        return userid

    async def check_permission(request: web.Request, permission: Union[str, enum.Enum],
                               context: Any = None) -> None:
        """Checker that passes only to authoraised users with given permission.

        If user is not authorized - raises HTTPUnauthorized,
        if user is authorized and does not have permission -
        raises HTTPForbidden.
        """

        await check_authorized(request)
        allowed = await permits(request, permission, context)
        if not allowed:
            raise web.HTTPForbidden(reason="User does not have '{}' permission".format(permission))

    def setup(app: web.Application, identity_policy: AbstractIdentityPolicy,
              autz_policy: AbstractAuthorizationPolicy) -> None:
        if not isinstance(identity_policy, AbstractIdentityPolicy):
            raise ValueError("Identity policy is not subclass of AbstractIdentityPolicy")
        if not isinstance(autz_policy, AbstractAuthorizationPolicy):
            raise ValueError("Authentication policy is not subclass of AbstractAuthorizationPolicy")

        app[IDENTITY_KEY] = identity_policy
        app[AUTZ_KEY] = autz_policy