LHC Tunnel

LHC Tunnel

Tuesday, 21 October 2014

Kerberos and Single Sign On with OpenStack

External Authentication with Keystone

One of the most commonly requested features by the CERN cloud user community is support for authentication using Kerberos on the command line and single-sign on with the OpenStack dashboard.

In our Windows and Linux environment, we run Active Directory to provide authentication services. During the Essex cycle of OpenStack, we added support for getting authentication based on Active Directory passwords. However, this had several drawbacks:
  • When using the command line clients, the users had the choice of storing their password in environment variables such as with the local openrc script or re-typing their password with each OpenStack command. Passwords in environment variables has significant security risks since they are passed to any sub-command and can be read by the system administrator of the server you are on.
  • When logging in with the web interface, the users were entering their password into the dashboard. Most of CERN's applications use a single sign on package with Active Directory Federation Services (ADFS). Recent problems such as Heartbleed show the risks of entering passwords into web applications.
The following describes how we configured this functionality.

Approach

With our upgrade to Icehouse completed last week, the new release of the v3 identity API, Keystone now supports several authentication mechanisms through plugins. By default password, token and external authentication were provided. In this scenario, other authentication methods such Kerberos or X.509 can be used with a proper apache configuration and the external plugin provided in keystone. Unfortunately, when enabling these methods on apache, there is no way to make them optional so the client can choose the most appropriate.

Also when checking the projects he can access, the client normally does two operations on keystone, one to retrieve the token, and the other one with the token to retrieve the project list. Even if it is specified in the environment variables, the second call always uses the catalog, so if in the catalog has version 2 and we are using version 3 then we have an exception while doing the API call.

Requirements

In this case we need a solution that allows us to use Kerberos, X.509 or another authentication mechanism in a transparent way and also backwards compatible, so we can offer both APIs and let the user choose which is the most appropriate for its workflow. This will allow us to migrate services from one API version to the next one with no downtime.

In order to allow external authentication to our clients, we need to cover two parts, client side and server side. Client side to distinguish which is the auth plugin to use, and Server side to allow multiple auth methods and API versions at once.

Server Solution

In order to have different entry points under the same api, we would need a load balancer, in this particular case we use HAproxy. From this load balancer we are calling two different sets of backend machines, one for version 2 of the API and the other for version 3. In this loadbalancer, we can analyze the version of the url where the client is connecting to so we can redirect him to the appropriate set. Each backend is running keystone under apachea and it is connected to the same database. We need this to allow tokens to be validated no matter the version is used on the client. The only difference between the backend sets is the catalog, the identity service is different on both pointing the client to the available version on each set. For this particular purpose we will use a templatedcatalog.


Right now we solve the multiversion issue of the OpenStack environment, but we didn't allow Kerberos or X.509. As these methods are not optional we may need different entry points for each authentication plugin used. So we need entry points for OpenStack authentication (password, token), Kerberos and X.509. There is no issue with the catalog if we enable these methods, all of them can be registered on the service catalog like normal OpenStack authentication, because any consequent call on the system will use token based authentication.
So in the apache v3 backend we have the following urls defined:

https://mykeystone/main/v3
https://mykeystone/admin/v3
https://mykeystone/krb/v3
https://mykeystone/x509/v3

If you post an authentication request to the Kerberos url, this will require a valid Kerberos token, in case it is not sent it will initiate a challenge. After validating it, it will it the user as the REMOTE_USER. In case of client certificate authentication, you will use the X.509 url that will require a valid certificate, in this case it will use the DN as the REMOTE_USER. After this variable is set, then Keystone can take over and check the user in the Keystone database.
There is a small caveat, we cannot do offloading of SSL client authentication on the HAproxy, so for this purpose we need to connect directly from the client, it uses a different port 8443 and connects directly to the backends configured. So for X.509 authentication we use 'https://mykeystone:8443/x509/v3'

Client Solution

For the client side, the plugin mechanism will only be available on the common cli (python-openstackclient) and not on the rest of the toolset (nova, glance, cinder, ...). There is no code yet that implements the plugin functionality, so in order to provide a short term implementation, and based on our current architecture, we can base it the selection of the plugin on the OS_AUTH_URL for the moment. The final upstream implementation will almost certainly differ at this point by using a parameter or discover the auth plugins available. In that case the client implementation may change but this is likely to be close to the initial implementation.

In openstackclient/common/clientmanager.py
...
        if 'krb' in auth_url and ver_prefix == 'v3':
            LOG.debug('Using kerberos auth %s', ver_prefix)
            self.auth = v3_auth_kerberos.Kerberos(
                auth_url=auth_url,
                trust_id=trust_id,
                domain_id=domain_id,
                domain_name=domain_name,
                project_id=project_id,
                project_name=project_name,
                project_domain_id=project_domain_id,
                project_domain_name=project_domain_name,
            )
        elif 'x509' in auth_url and ver_prefix == 'v3':
            LOG.debug('Using x509 auth %s', ver_prefix)
            self.auth = v3_auth_x509.X509(
                auth_url=auth_url,
                trust_id=trust_id,
                domain_id=domain_id,
                domain_name=domain_name,
                project_id=project_id,
                project_name=project_name,
               project_domain_id=project_domain_id,
                project_domain_name=project_domain_name,
                client_cert=client_cert,
            )
        elif self._url:
...

HAproxy configuration

global
  chroot  /var/lib/haproxy
  daemon
  group  haproxy
  log  mysyslogserver local0
  maxconn  8000
  pidfile  /var/run/haproxy.pid
  ssl-default-bind-ciphers  ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-AES256-GCM-SHA384:DHE-RSA-AES128-GCM-SHA256:DHE-DSS-AES128-GCM-SHA256:kEDH+AESGCM:ECDHE-RSA-AES128-SHA256:ECDHE-ECDSA-AES128-SHA256:ECDHE-RSA-AES128-SHA:ECDHE-ECDSA-AES128-SHA:ECDHE-RSA-AES256-SHA384:ECDHE-ECDSA-AES256-SHA384:ECDHE-RSA-AES256-SHA:ECDHE-ECDSA-AES256-SHA:DHE-RSA-AES128-SHA256:DHE-RSA-AES128-SHA:DHE-DSS-AES128-SHA256:DHE-RSA-AES256-SHA256:DHE-DSS-AES256-SHA:DHE-RSA-AES256-SHA:AES128-GCM-SHA256:AES256-GCM-SHA384:AES128:AES256:AES:!aNULL:!eNULL:!EXPORT:!DES:!RC4:!MD5:!PSK
  stats  socket /var/lib/haproxy/stats
  tune.ssl.default-dh-param  2048
  user  haproxy

defaults
  log  global
  maxconn  8000
  mode  http
  option  redispatch
  option  http-server-close
  option  contstats
  retries  3
  stats  enable
  timeout  http-request 10s
  timeout  queue 1m
  timeout  connect 10s
  timeout  client 1m
  timeout  server 1m
  timeout  check 10s

frontend cloud_identity_api_production
  bind 188.184.148.158:443 ssl no-sslv3 crt /etc/haproxy/cert.pem verify none
  acl  v2_acl_admin url_beg /admin/v2
  acl  v2_acl_main url_beg /main/v2
  default_backend  cloud_identity_api_v3_production
  timeout  http-request 5m
  timeout  client 5m
  use_backend  cloud_identity_api_v2_production if v2_acl_admin
  use_backend  cloud_identity_api_v2_production if v2_acl_main

frontend cloud_identity_api_x509_production
  bind 188.184.148.158:8443 ssl no-sslv3 crt /etc/haproxy/cert.pem ca-file /etc/haproxy/ca.pem verify required
  default_backend  cloud_identity_api_v3_production
  rspadd  Strict-Transport-Security:\ max-age=15768000
  timeout  http-request 5m
  timeout  client 5m
  use_backend  cloud_identity_api_v3_production if { ssl_fc_has_crt }

backend cloud_identity_api_v2_production
  balance  roundrobin
  stick  on src
  stick-table  type ip size 20k peers cloud_identity_frontend_production
  timeout  server 5m
  timeout  queue 5m
  timeout  connect 5m
  server cci-keystone-bck01 128.142.132.22:443 check ssl verify none
  server cci-keystone-bck02 188.184.149.124:443 check ssl verify none
  server p01001453s11625 128.142.174.37:443 check ssl verify none

backend cloud_identity_api_v3_production
  balance  roundrobin
  http-request  set-header X-SSL-Client-CN %{+Q}[ssl_c_s_dn(cn)]
  stick  on src
  stick-table  type ip size 20k peers cloud_identity_frontend_production
  timeout  server 5m
  timeout  queue 5m
  timeout  connect 5m
  server cci-keystone-bck03 128.142.159.38:443 check ssl verify none
  server cci-keystone-bck04 128.142.164.244:443 check ssl verify none
  server cci-keystone-bck05 128.142.132.192:443 check ssl verify none
  server cci-keystone-bck06 128.142.146.182:443 check ssl verify none

listen stats
  bind 188.184.148.158:8080
  stats  uri /
  stats  auth haproxy:NOTAPASSWORD

peers cloud_identity_frontend_production
  peer cci-keystone-load01.cern.ch 188.184.148.158:7777
  peer cci-keystone-load02.cern.ch 128.142.153.203:7777
  peer p01001464675431.cern.ch 128.142.190.8:7777
Apache configuration
WSGISocketPrefix /var/run/wsgi

Listen 443

<VirtualHost *:443>
  ServerName keystone.cern.ch
  DocumentRoot /var/www/cgi-bin/keystone
  LimitRequestFieldSize 65535

  SSLEngine On
  SSLCertificateFile      /etc/keystone/ssl/certs/hostcert.pem
  SSLCertificateKeyFile   /etc/keystone/ssl/keys/hostkey.pem
  SSLCertificateChainFile /etc/keystone/ssl/certs/ca.pem
  SSLCACertificateFile    /etc/keystone/ssl/certs/ca.pem
  SSLVerifyClient         none
  SSLOptions              +StdEnvVars
  SSLVerifyDepth          10
  SSLUserName             SSL_CLIENT_S_DN_CN
  SSLProtocol             all -SSLv2 -SSLv3

  SSLCipherSuite          ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-AES256-GCM-SHA384:DHE-RSA-AES128-GCM-SHA256:DHE-DSS-AES128-GCM-SHA256:kEDH+AESGCM:ECDHE-RSA-AES128-SHA256:ECDHE-ECDSA-AES128-SHA256:ECDHE-RSA-AES128-SHA:ECDHE-ECDSA-AES128-SHA:ECDHE-RSA-AES256-SHA384:ECDHE-ECDSA-AES256-SHA384:ECDHE-RSA-AES256-SHA:ECDHE-ECDSA-AES256-SHA:DHE-RSA-AES128-SHA256:DHE-RSA-AES128-SHA:DHE-DSS-AES128-SHA256:DHE-RSA-AES256-SHA256:DHE-DSS-AES256-SHA:DHE-RSA-AES256-SHA:AES128-GCM-SHA256:AES256-GCM-SHA384:AES128:AES256:AES:!aNULL:!eNULL:!EXPORT:!DES:!RC4:!MD5:!PSK
  SSLHonorCipherOrder     on
  Header add Strict-Transport-Security "max-age=15768000"


  WSGIDaemonProcess keystone user=keystone group=keystone processes=2 threads=2
  WSGIProcessGroup keystone

  WSGIScriptAlias /admin /var/www/cgi-bin/keystone/admin
  <Location "/admin">
    SSLRequireSSL
    SSLVerifyClient       none
  </Location>

  WSGIScriptAlias /main /var/www/cgi-bin/keystone/main
  <Location "/main">
    SSLRequireSSL
    SSLVerifyClient       none
  </Location>

  WSGIScriptAlias /krb /var/www/cgi-bin/keystone/main

  <Location "/krb">
    SSLRequireSSL
    SSLVerifyClient       none
  </Location>

  <Location "/krb/v3/auth/tokens">
    SSLRequireSSL
    SSLVerifyClient       none
    AuthType              Kerberos
    AuthName              "Kerberos Login"
    KrbMethodNegotiate    On
    KrbMethodK5Passwd     Off
    KrbServiceName        Any
    KrbAuthRealms         CERN.CH
    Krb5KeyTab            /etc/httpd/http.keytab
    KrbVerifyKDC          Off
    KrbLocalUserMapping   On
    KrbAuthoritative      On
    Require valid-user
  </Location>

  WSGIScriptAlias /x509 /var/www/cgi-bin/keystone/main

  <Location "/x509">
    Order allow,deny
    Allow from all
  </Location>

  WSGIScriptAliasMatch ^(/main/v3/OS-FEDERATION/identity_providers/.*?/protocols/.*?/auth)$ /var/www/cgi-bin/keystone/main/$1

  <LocationMatch /main/v3/OS-FEDERATION/identity_providers/.*?/protocols/saml2/auth>
    ShibRequestSetting requireSession 1
    AuthType shibboleth
    ShibRequireSession On
    ShibRequireAll On
    ShibExportAssertion Off
    Require valid-user
  </LocationMatch>

  <LocationMatch /main/v3/OS-FEDERATION/websso>
    ShibRequestSetting requireSession 1
    AuthType shibboleth
    ShibRequireSession On
    ShibRequireAll On
    ShibExportAssertion Off
    Require valid-user
  </LocationMatch>

  <Location /Shibboleth.sso>
    SetHandler shib
  </Location>

  <Directory /var/www/cgi-bin/keystone>
    Options FollowSymLinks
    AllowOverride All
    Order allow,deny
    Allow from all
  </Directory>
</VirtualHost>

References

The code of python-openstackclient as long as the python-keystoneclient that we are using for this implementation is available at:


We will be working with the community in the Paris summit to find the best way to integrate this functionality into the standard OpenStack release.

Credits

The main author is Jose Castro Leon with help from Marek Denis.

Many thanks to the Keystone core team for their help and advice on the implementation.

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