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# Copyright (c) 2013, Michael Komitee
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"""Kerberos authentication module"""
import logging
import os
from functools import wraps
from socket import getfqdn
from typing import Any, Callable, Optional, Tuple, TypeVar, Union, cast

import kerberos
from flask import Response, _request_ctx_stack as stack, g, make_response, request  # type: ignore
from requests_kerberos import HTTPKerberosAuth

from airflow.configuration import conf

log = logging.getLogger(__name__)


CLIENT_AUTH: Optional[Union[Tuple[str, str], Any]] = HTTPKerberosAuth(service='airflow')


class KerberosService:
    """Class to keep information about the Kerberos Service initialized"""

    def __init__(self):
        self.service_name = None


# Stores currently initialized Kerberos Service
_KERBEROS_SERVICE = KerberosService()


def init_app(app):
    """Initializes application with kerberos"""
    hostname = app.config.get('SERVER_NAME')
    if not hostname:
        hostname = getfqdn()
    log.info("Kerberos: hostname %s", hostname)

    service = 'airflow'

    _KERBEROS_SERVICE.service_name = f"{service}@{hostname}"

    if 'KRB5_KTNAME' not in os.environ:
        os.environ['KRB5_KTNAME'] = conf.get('kerberos', 'keytab')

    try:
        log.info("Kerberos init: %s %s", service, hostname)
        principal = kerberos.getServerPrincipalDetails(service, hostname)
    except kerberos.KrbError as err:
        log.warning("Kerberos: %s", err)
    else:
        log.info("Kerberos API: server is %s", principal)


def _unauthorized():
    """
    Indicate that authorization is required
    :return:
    """
    return Response("Unauthorized", 401, {"WWW-Authenticate": "Negotiate"})


def _forbidden():
    return Response("Forbidden", 403)


def _gssapi_authenticate(token):
    state = None
    ctx = stack.top
    try:
        return_code, state = kerberos.authGSSServerInit(_KERBEROS_SERVICE.service_name)
        if return_code != kerberos.AUTH_GSS_COMPLETE:
            return None
        return_code = kerberos.authGSSServerStep(state, token)
        if return_code == kerberos.AUTH_GSS_COMPLETE:
            ctx.kerberos_token = kerberos.authGSSServerResponse(state)
            ctx.kerberos_user = kerberos.authGSSServerUserName(state)
            return return_code
        if return_code == kerberos.AUTH_GSS_CONTINUE:
            return kerberos.AUTH_GSS_CONTINUE
        return None
    except kerberos.GSSError:
        return None
    finally:
        if state:
            kerberos.authGSSServerClean(state)


T = TypeVar("T", bound=Callable)


def requires_authentication(function: T):
    """Decorator for functions that require authentication with Kerberos"""

    @wraps(function)
    def decorated(*args, **kwargs):
        header = request.headers.get("Authorization")
        if header:
            ctx = stack.top
            token = ''.join(header.split()[1:])
            return_code = _gssapi_authenticate(token)
            if return_code == kerberos.AUTH_GSS_COMPLETE:
                g.user = ctx.kerberos_user
                response = function(*args, **kwargs)
                response = make_response(response)
                if ctx.kerberos_token is not None:
                    response.headers['WWW-Authenticate'] = ' '.join(['negotiate', ctx.kerberos_token])

                return response
            if return_code != kerberos.AUTH_GSS_CONTINUE:
                return _forbidden()
        return _unauthorized()

    return cast(T, decorated)
