2020-02-20 00:28:43 -05:00
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import base64
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import binascii
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import hashlib
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import hmac
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import logging
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import os
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import struct
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2020-02-20 03:15:32 -05:00
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import time
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2021-04-25 04:12:52 -04:00
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from typing import Optional
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2020-02-20 00:28:43 -05:00
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import gssapi
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import ldap
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2020-02-20 03:15:32 -05:00
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from flask import Flask, Response, redirect, request
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from gssapi.exceptions import BadMechanismError, GSSError, GeneralError
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2020-03-09 02:24:43 -04:00
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from werkzeug.routing import Rule
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2020-02-20 00:28:43 -05:00
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app = Flask(__name__)
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app.logger.setLevel(logging.INFO)
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2021-08-21 17:14:44 -04:00
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app.url_map.add(Rule('/krbauth', endpoint='krbauth.auth'))
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2020-03-09 02:24:43 -04:00
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app.url_map.add(Rule('/krbauth/check', endpoint='krbauth.check'))
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2020-02-20 00:28:43 -05:00
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timestamp = struct.Struct('!q')
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hmac_digest = hashlib.sha512
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digest_size = hmac_digest().digest_size
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HMAC_KEY = os.environ['KRBAUTH_HMAC_KEY'].encode('utf-8')
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DURATION = int(os.environ.get('KRBAUTH_KEY_DURATION', 3600))
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RANDOM_SIZE = int(os.environ.get('KRBAUTH_RANDOM_SIZE', 32))
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2020-02-20 02:55:19 -05:00
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LDAP_SERVER = os.environ.get('KRBAUTH_LDAP_SERVER')
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2020-02-20 00:28:43 -05:00
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LDAP_BIND_DN = os.environ.get('KRBAUTH_LDAP_BIND_DN')
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LDAP_BIND_AUTHTOK = os.environ.get('KRBAUTH_LDAP_BIND_AUTHTOK')
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2020-02-20 02:55:19 -05:00
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LDAP_SEARCH_BASE = os.environ.get('KRBAUTH_LDAP_SEARCH_BASE')
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2020-02-20 03:05:29 -05:00
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LDAP_USER_DN = os.environ.get('KRBAUTH_LDAP_USER_DN')
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assert not LDAP_USER_DN or LDAP_USER_DN.count('%s') == 1
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2020-02-20 00:28:43 -05:00
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GSSAPI_NAME = os.environ.get('KRBAUTH_GSSAPI_NAME')
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if GSSAPI_NAME:
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gssapi_name = gssapi.Name(GSSAPI_NAME, gssapi.NameType.hostbased_service)
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gssapi_creds = gssapi.Credentials(name=gssapi_name, usage='accept')
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else:
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gssapi_creds = None
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COOKIE_SECURE = os.environ.get('KRBAUTH_SECURE_COOKIE', '1').lower() not in ('0', 'no')
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class Context:
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2021-04-25 04:12:52 -04:00
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def __init__(self, ldap_group: Optional[str]) -> None:
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2020-02-20 00:28:43 -05:00
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self.ldap_group = ldap_group
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@classmethod
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2021-04-25 04:12:52 -04:00
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def from_request(cls) -> 'Context':
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2020-02-20 00:28:43 -05:00
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return cls(ldap_group=request.environ.get('KRBAUTH_LDAP_GROUP'))
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2021-04-25 04:12:52 -04:00
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def bytes(self) -> bytes:
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assert self.ldap_group
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2020-02-20 00:28:43 -05:00
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return ''.join([self.ldap_group]).encode('utf-8')
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2021-04-25 04:12:52 -04:00
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def make_cookie(context: Context) -> bytes:
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2020-02-20 00:28:43 -05:00
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message = timestamp.pack(int(time.time()) + DURATION) + os.urandom(RANDOM_SIZE) + context.bytes()
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signature = hmac.new(HMAC_KEY, message, hmac_digest).digest()
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return base64.b64encode(signature + message)
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2021-04-25 04:12:52 -04:00
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def verify_cookie(cookie: Optional[str], context: Context) -> bool:
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2020-02-20 00:28:43 -05:00
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if not cookie:
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return False
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try:
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data = base64.b64decode(cookie)
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signature = data[:digest_size]
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message = data[digest_size:]
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ts = timestamp.unpack(message[:timestamp.size])[0]
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except (struct.error, binascii.Error):
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return False
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if ts < time.time():
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return False
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if not hmac.compare_digest(message[timestamp.size + RANDOM_SIZE:], context.bytes()):
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return False
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2020-07-04 15:40:06 -04:00
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expected = hmac.new(HMAC_KEY, message, hmac_digest).digest()
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2020-02-20 00:28:43 -05:00
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return hmac.compare_digest(expected, signature)
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2021-04-25 04:12:52 -04:00
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def make_401(reason: str, negotiate: Optional[str] = 'Negotiate', **kwargs) -> Response:
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2020-02-20 03:05:29 -05:00
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app.logger.info('Returning unauthorized: %s (%s)', reason, kwargs)
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resp = Response('''\
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2020-02-20 00:28:43 -05:00
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<html>
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<head>
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<title>401 Unauthorized</title>
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</head>
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<body>
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<center><h1>401 Unauthorized</h1></center>
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<hr>
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<center>%s</center>
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</body>
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</html>
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2020-02-20 03:05:29 -05:00
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''' % (reason,), status=401)
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2020-05-03 01:06:40 -04:00
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if negotiate:
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2020-02-20 03:05:34 -05:00
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resp.headers.add('WWW-Authenticate', negotiate)
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2020-02-20 03:05:29 -05:00
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if LDAP_USER_DN:
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resp.headers.add('WWW-Authenticate', 'Basic')
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return resp
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2020-02-20 00:28:43 -05:00
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2021-04-25 04:12:52 -04:00
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def auth_success(context: Context, next_url: str) -> Response:
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resp = redirect(next_url, code=307, Response=Response)
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2020-02-20 03:05:29 -05:00
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resp.set_cookie('krbauth', make_cookie(context), secure=COOKIE_SECURE, httponly=True, samesite='Strict')
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return resp
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2020-02-20 00:28:43 -05:00
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2021-04-25 04:12:52 -04:00
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def auth_spnego(context: Context, next_url: str) -> Response:
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try:
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in_token = base64.b64decode(request.headers['Authorization'][len('Negotiate '):])
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2020-02-20 00:28:43 -05:00
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except binascii.Error:
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return Response(status=400)
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try:
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krb5_ctx = gssapi.SecurityContext(creds=gssapi_creds, usage='accept')
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out_token = krb5_ctx.step(in_token)
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if not krb5_ctx.complete:
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return make_401('Negotiation in progress',
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negotiate=f'Negotiate {base64.b64encode(out_token).decode("ascii")}')
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2020-02-20 00:28:43 -05:00
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2021-04-25 04:12:52 -04:00
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krb5_name = krb5_ctx.initiator_name
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2020-02-20 03:05:34 -05:00
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except BadMechanismError:
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return make_401('GSSAPI mechanism not supported', negotiate=None)
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2020-02-20 00:28:43 -05:00
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except (GSSError, GeneralError) as e:
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return make_401(str(e))
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2020-02-20 00:28:43 -05:00
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2020-02-20 02:55:19 -05:00
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if LDAP_SERVER and LDAP_SEARCH_BASE and context.ldap_group:
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2020-02-20 00:28:43 -05:00
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ldap_ctx = ldap.initialize(LDAP_SERVER)
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if LDAP_BIND_DN and LDAP_BIND_AUTHTOK:
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ldap_ctx.bind_s(LDAP_BIND_DN, LDAP_BIND_AUTHTOK, ldap.AUTH_SIMPLE)
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ldap_filter = '(&(memberOf=%s)(krbPrincipalName=%s))' % (context.ldap_group, krb5_name)
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2020-02-20 03:05:29 -05:00
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result = ldap_ctx.search_s(LDAP_SEARCH_BASE, ldap.SCOPE_SUBTREE, ldap_filter, ['cn'])
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2020-02-20 00:28:43 -05:00
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if not result:
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return make_401('Did not find LDAP group member', krb5_name=krb5_name)
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2020-02-20 03:05:29 -05:00
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app.logger.info('Authenticated via Kerberos as: %s, %s', krb5_name, result[0][0])
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2020-02-20 00:28:43 -05:00
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else:
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2020-02-20 03:05:29 -05:00
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app.logger.info('Authenticated via Kerberos as: %s', krb5_name)
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2020-02-20 00:28:43 -05:00
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2020-02-20 03:05:29 -05:00
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return auth_success(context, next_url)
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2021-04-25 04:12:52 -04:00
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def auth_basic(context: Context, next_url: str) -> Response:
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2020-02-20 03:05:29 -05:00
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try:
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token = base64.b64decode(request.headers['Authorization'][6:])
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username, _, password = token.decode('utf-8').partition(':')
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except (binascii.Error, UnicodeDecodeError):
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return Response(status=400)
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2020-02-20 03:05:34 -05:00
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if not username or not password:
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return make_401('Invalid username or password')
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2020-02-20 03:05:34 -05:00
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2021-04-25 04:12:52 -04:00
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assert LDAP_USER_DN is not None
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2020-02-20 03:05:29 -05:00
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dn = LDAP_USER_DN % (username,)
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ldap_ctx = ldap.initialize(LDAP_SERVER)
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try:
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ldap_ctx.bind_s(dn, password)
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except ldap.INVALID_CREDENTIALS:
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2021-04-25 04:12:52 -04:00
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return make_401('Failed to authenticate to LDAP', dn=dn)
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2020-02-20 03:05:29 -05:00
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if context.ldap_group:
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if not ldap_ctx.search_s(dn, ldap.SCOPE_BASE, '(memberof=%s)' % (context.ldap_group,)):
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2021-04-25 04:12:52 -04:00
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return make_401('Did not find LDAP group member', dn=dn, group=context.ldap_group)
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2020-02-20 03:05:29 -05:00
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app.logger.info('Authenticated via LDAP as: %s in %s', dn, context.ldap_group)
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else:
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app.logger.info('Authenticated via LDAP as: %s', dn)
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return auth_success(context, next_url)
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2021-08-21 17:14:44 -04:00
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@app.endpoint('krbauth.auth')
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def auth() -> Response:
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2020-02-20 03:05:29 -05:00
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next_url = request.args.get('next', '/')
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context = Context.from_request()
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authorization = request.headers.get('Authorization', '')
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if authorization.startswith('Negotiate '):
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return auth_spnego(context, next_url)
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if LDAP_USER_DN and authorization.startswith('Basic '):
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return auth_basic(context, next_url)
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2021-04-25 04:12:52 -04:00
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return make_401('No Authorization header sent')
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2020-02-20 00:28:43 -05:00
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2020-03-09 02:24:43 -04:00
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@app.endpoint('krbauth.check')
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2021-04-25 04:12:52 -04:00
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def check() -> Response:
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2020-02-20 00:28:43 -05:00
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if verify_cookie(request.cookies.get('krbauth'), Context.from_request()):
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return Response(status=200)
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return Response(status=401)
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