HAProxy Enterprise Documentation 12.5

Active Directory

The HAProxy Single Sign-On solution allows you to set up SSO on a Microsoft Active Directory domain.

It can optionally use the Kerberos protocol for authentication. It is also compatible with Microsoft Active Directory or OpenLDAP servers.

It is composed of a set of configuration files, and a program called spoa-sso, which talks to HAProxy using the SPOE (Stream Processing Offload Engine) protocol.

SSO allows you to:

  • Implement access control to applications on your network, even if the applications themselves do not support authentication or the Kerberos protocol.

  • Implement access control and identity delegation to your internal applications, from an external network or from a VPN.

  • Provide Single Sign On ability in a Microsoft Active Directory Domain.

Terms Used

The SSO solution allows users to access different resources and applications, depending on their rights.

  • In a Microsoft environment, users of an organization are part of a domain.

  • Active Directory is a set of services that provide authentication, identification, and management of users of a domain.

Active Directory also deals with these protocols within the domain:

  • DNS

  • LDAP

  • Kerberos

Note

If you use Microsoft Active Directory, it becomes a central part of the SSO solution. Hence, you must set it up correctly for proper operation. See Active Directory documentation for information.

Kerberos protocol

This SSO solution optionally implements the S4U (services for user) extensions from Microsoft that allow enhanced security and user impersonation.

It supports SPNEGO negotiation mechanism.

Refer to the following documents for more information:

DNS Protocol

To use successfully the Kerberos protocol, you must observe some requirements regarding the DNS configuration:

  • The server running the SSO agent must have a proper hostname that can be resolved to an IP, using DNS.

  • You can also modify your /etc/hosts file

  • The IP address of the Kerberos KDC is retrieved via DNS, using "_kerberos" service.

  • If you cannot configure your DNS server, you must specify the KDC in /etc/krb5.conf.

  • The reverse DNS must also work. If not, you must add /etc/krb.conf to disable the reverse DNS:

    [libdefaults]
    
    rdns = false

HAProxy, SPOE protocol, and SSO agent

The SSO agent uses HAProxy's Stream Processing Offload Engine protocol (SPOA).

It requires HAProxy 1.7r2 or greater or 1.8 or greater. The SSO agent is independent from HAProxy and runs as a separate process.

Each HTTP request and response is passed to the SSO agent which checks if the user is allowed to access the requested resource and determines whether to:

  • Allow

  • Deny

  • Present the authentication form

Single Sign On flowchart 1 Single Sign On flowchart 2

Setting up SSO

In ALOHA, you can either:

  • Use the template from the LB "Admin" tab.

  • Configure manually SSO, as follows:

    1. Refer to the section Configure SSO

    2. Add backends for each of your applications.

    3. You can enable verbose debugging of the SSO agent, as follows:

      config set sso debug '--debug-all'
    4. Enable SSO:

      config set haproxy sso 1
      config sso set autostart 1
      service sso start
    5. Restart HAProxy:

      service haproxy restart

Installation

Using the provided built-in Web portal

If you use the default built-in Web portal, you can customize your company logo and your CSS file.

The location of these files is:

  • /etc/haproxy/sso/portal/logo.png (or logo.jpg)

  • /etc/haproxy/sso/portal/css.css

Implementing a custom Web portal

To implement a Web portal that displays a login form to the user, you only need a simple Web server that handles HTTP headers sent by HAProxy.

HAProxy headers

Header

Description

X-SSO-ACTION

An action that can be any of the following:

  • frm: display the authentication form to the user

  • fOK: display the login confirmation page: You now have access to application {%app%}

  • lOK: display the logout confirmation page: You have been logged out

  • dny: access denied

  • err: an error occurred

X-SSO-MSG

A message to display to the user

X-SSO-DOMAIN

The domain

X-SSO-APP

The application that the user wants to access. It is determined by the URL and the SSO agent.

X-SSO-TITLE-PAGE

The main URL of the application. The web server can include a link to this page to lead the user directly to the application.

X-SSO-LOGIN (SSO >= v1.2 or ALOHA >= 10.5.6)

If set_login option is set to 1, this header will contain the user login.

X-SSO-REDIR_QS (SSO >= v1.2 or ALOHA >= 10.5.6)

This header redirects users to the page they want to access before being redirected to the authentication portal.

  • If this header is set, the server must include its content into the form the user will POST.

  • For example, you can add a hidden field. This field must be called posted_redir.

X-SSO-REDIR_URL (SSO >= v1.2 or ALOHA >= 10.5.6)

Contains the URL that users want to access. You can redirect them to this URL after a successful authentication.

Establish an authentication form

This HTML page must contain an HTML form to allow the user to enter his login and password and to select the domain to log on.

The POST action must be able to post on the same URL.

A minimal form could be the following:

<form method="POST">
  <input name="login" />
  <input name="password" />
  <select name="domain">
    <option value="mydomain.net">My Domain</option>
  </select>
  <!-- optional field. It should contain the value extracted from the
  X-SSO-REDIR_QS header -->
  <input type="hidden" name="posted_redir" values="..." />
</form>

The POST is done on the form backend and handled by HAProxy, which extracts the information and passes it on to the SSO agent.

Add SSO ability to an application

After you set up SSO, use the following procedure to add more applications:

  1. Add a new domain:

    • You must add the new domain in a Web form of an HTML page. The user must be able to select it, and you must include its value in the POST.

  2. To add an application if you use Kerberos with an Active Directory:

    • Add a new service user associated with the service principal name (SPN) of your application.

    • Create a new Keytab for the new SPN or add it to an existing Keytab.

      On Windows:

      ktpass /out myapp.keytab /mapuser
      <service-user>MYDOMAIN.NET /princ
      HTTP/myapp.mydonain.net@MYDOMAIN.NET /pass <PASSWORD>
  3. Update the keytab_file directive, if needed.

  4. Add the application to conf/sso.map.

  5. In the configuration file so.ini, add the application section and attach it to the correct domain.

  6. Add the specified backend to haproxy.cfg.

  7. To check if a user is allowed to access an application, you must check that the X-SSO-* headers are as follows:

    • X-SSO-APP: <name of the application>

    • X-SSO-DOMAIN: <name of the domain>

    • X-SSO-ACTION: alw

    • X-SSO-LOGIN: <user login> (SSO >= v1.2 or ALOHA >= 10.5.6)

Configuration

The single sign-on (SSO) function requires several configuration files.

On the ALOHA, you can use the templates that ALOHA provides to generate automatically your configuration.

Below is an explanation of each configuration file.

Configure SSO

The file haproxy-sso.cfg defines the main HTTP frontend that HTTP clients require in order to use SSO.

It also defines the HTTP rules, ACLs, and checks involved between the SPOE agent and HAProxy.

You may have to modify parts of this file depending on your Active Directory setup and your network configuration.

  • The bind directive of the frontend: bind *:80

  • The sso_portal backend:

    • If you use your own external Web server to host the SSO portal, use:

      backend sso_portal
         # this is the webserver used to diplay the SSO login form
         mode http
         server sso_portal-1 my_web_server:80
    • If you want to use the built-in LUA Web server, use:

      global
         lua-load sso_portal.lua
         # ...
      
      backend sso_portal
         mode http
         http-request use-service lua.sso_portal

Configure SSO SPOE

The haproxy-sso-spoe.cfg file contains information regarding which messages to exchange between the SSO SPOE daemon and HAProxy.

We recommend that you do not modify it and keep it as provided.

Specify SSO mappings

The file sso.map must contain the mappings between your different applications and the Host header.

# Host header                      <domain>/<app>
sp2010.mydomain.net                2010.mydomain.net/sharepoint2010
sp2013.mydomain.net                2013.mydomain.net/sharepoint2013
exchange2013.mydomain.net          2013.mydomain.net/exchange2013
stats.mydomain.net                 stats/stats

Configure the SSO daemon

The sso.ini file is the main configuration file of the SSO daemon. It must contain information about each application that you want to manage.

It uses a similar syntax to any typical Windows .ini file.

  • Lines starting with ; or # are comments.

  • Comments can appear at the end of any line when preceded by a space.

  • There are several sections in sso.ini:

    • The default section ([defaults]) contains default values. These values are inherited by each domain.

    • Domain sections ([domain:mydomain]) define properties valid for the scope of the entire domain.

    • Other sections are applications sections.

  • At least one domain section is required, and each application must be attached to exactly one domain. Applications inherit the properties of their domain, and can also override them.

  • Some properties can include keywords within brackets such as <KRB_REALM> that get replaced with appropriate values at run time. For example, if you prefer that all your backends start with bk_, you can use:

    backend = bk_<APP_NAME>

Configuration directives

Directive

Description

[application_name]

Each application must have a unique name. To name applications, you may use alphanumeric characters or underscores. This name must match a name in the sso.map file.

internal_domain

The internal host name of your application. It must match the domain part of the Kerberos SPN (ie HTTP/mydomain.int)

external_domain

The external FQDN of your application.

krb_auth_method

When setting this field to 1, HAProxy authenticates the user with the information provided in the login form. This is the methode we recommend, in addition to krb_s4u = 1 that uses Kerberos constrained delegation.

krb_cache_name

Allows you to choose the location of the Kerberos tickets cache:

  • on disk: /tmp/kr5cc_<USER>

  • in memory: MEMORY:kr5cc_<USER>

sso_cookie_domain

Defines the domain attribute that the SSO agent must use when setting its cookie. You must match the longest common part of your external host name.

  • sso_cookie_lifetime: Defines the lifetime of the SSO cookie (in seconds)

  • Past this time, the user must reauthenticate.

  • Default: 36000s.

sso_cookie_lifetime

Defines the lifetime of the SSO cookie (in seconds). Past this time, the user must reauthenticate. Default: 36000s.

ldap_uri

For each domain, you must define additional LDAP and Kerberos parameters as follows: ldap://ad.mydomain.net.

  • The LDAP server validates the credentials from the user, and refreshes all groups to which the user belongs.

  • HAProxy refreshes a group membership every ldap_groups_refresh_interval seconds, and it can use a different user/password specified in ldap_groups_refresh_user and ldap_groups_refresh_password.

    • ldap_base, such as dc=mydomain,dc=net

    • krb_realm contains your Kerberos realm (usually in upper case)

    • krb_keytab_file defines the Keytab file that contains Kerberos services you want to use

ldap_auth_start_tls

Controls whether to use TLS when connecting to the LDAP server: 0:disabled, 1:enabled (by default)

internal_domain, external_domain

Must be defined for each application.

auth_url

Indicates the URLs to reach the login. When users must enter their credentials, HAProxy redirects them here.

  • After a successful authentication, a message displays with a link to access the application. You can use title_page to define the target of the link.

  • If your application runs on a non-standard port, you have to specify it in auth_url. For instance, if your application runs on port 8080, specify auth_url = <EXTERNAL_DOMAIN>:8080/auth.

logout_url (SSO >= v1.2 or ALOHA >= 10.5.6)

An authenticated user who reaches this URL gets logged out.

title_page

After a successful authentication, a message displays with a link to access the application.

  • You can use title_page to define the target of the link.

  • You must use an absolute URL with the scheme (HTTP or HTTPS).

  • Example: the URL for a standard Sharepoint2013 installation can be: https://<EXTERNAL_DOMAIN>/SitePages/Home.aspx.

redir_url_encoding_secret (SSO >= v1.2 or ALOHA >= 10.5.6)

Secret used to encode the current user URL, and to redirect the user after a successful authentication.

  • If you load-balance the SSO portal, you must share the secret among the different servers.

  • Otherwise, use <RANDOM> to generate a random secret upon launch, or <DISABLED> to disable the redirections.

ldap_required_group

Use this directive to restrict access to a particular application to a specified group of users.

  • The group must have the following form: CN=Builtin,DC=2013,DC=mydomain,DC=net.

  • HAProxy performs the matching using the memberOf attribute, which is case insensitive.

allow_unauthenticated_users

By default, all applications require the user to log into the corresponding domain and a valid cookie to grant access.

  • This directive allows access to certain applications without any access check.

  • If set to 1, HAProxy allows access without any access check.

set_login (SSO >= v1.2 or ALOHA >= 10.5.6)

If set to 1, sets the X-SSO-LOGIN header with the user login. Default: 0.

ldap_groups_membership_attribute (SSO >= v1.2.3)

LDAP member to search for when computing LDAP groups membership (default: memberOf)

ldap_groups_search_filter (SSO >= v1.2.3)

LDAP filter to apply when computing LDAP groups membership (default: sAMAccountName=<LOGIN>)

Diagnostics and troubleshooting

LDAP and Kerberos issues

The SSO solution does not require the file /etc/krb5.conf, but you can use it if the file is present in order to override default values or define a specific set of ciphers.

Refer to the MIT Kerberos documentation for more information.

To troubleshoot your environment, you can perform the following tasks:

  • Set the environment variable KRB5_TRACE to a log file, or to /dev/stdout to get more verbose Kerberos diagnostics. In addition, you can pass the --debug-krb flag to the SSO daemon.

  • Use the provided tool called sso-diag to test parts of the workflows involved when working with Kerberos.

  • Test ticket creation in Kerberos using: ./sso-diag -f sso.ini -a MYAPP -d MYDOMAIN -u USER -p PASSWORD krb_ticket

  • Check that your access rules or required LDAP groups are set and configured correctly by launching: ./sso-diag -f sso.ini -a MYAPP -d MYDOMAIN -u USER -p PASS auth and replacing MYAPP, MYDOMAIN, USER, and PASS with appropriate values. This directive simulates a user doing a POST on the authentication form with the supplied credentials.

  • You can also use ./sso-diag -f sso.ini -a MYAPP -d MYDOMAIN -A MYAPP2 -D MYDOMAIN2 -u USER -p PASS check to simulate a POST with the supplied credentials on MYAPP on MYDOMAIN, and then try to access MYAPP2 on MYDOMAIN2.

  • Get the status of the different worker threads running on the SSO agent by sending a SIGUSR1 at any time (when launched with --debug-all).

HAProxy 503 error

  • If you get a 503 error (service unavailable) coming from HAProxy, launch the agent with the --debug-spoe-variables option.

  • If the SSO application granted access to the URL, check that your backend is correctly configured in haproxy.cfg.

  • For example, if you get any of the following messages, check that the POC backend exists in the file haproxy.cfg:

    Encode SPOE set-var str scope=1 sso_app=poc
    Encode SPOE set-var str scope=1 sso_domain=poc
    Encode SPOE set-var str scope=1 action=alw
    Encode SPOE set-var str scope=2 backend=poc

Configuration errors

Message: Invalid domain xxx: 'cannot match config'

  • This means that the domain, which was set using sso.map by matching the host header, has no corresponding section in sso.ini.

Message: 'No authentication info found' displays repeatedly while

logging on the form

  • If you get this error, check the sso_cookie_domain directive in sso.ini.

  • The sso_cookie_domain must match the domain of your applications.

  • When logging in with correct credentials, you should see a response header similar to this:

    Set-Cookie: sso-cookie=abc122342; domain=mydomain.net

No server contact error

Message: 'Cannot contact server' or 'error in start_tls()'

  • Check that you configured your DNS correctly, and that you can reach the LDAP server on the correct port (standard ports are 636 or 389 depending on the configuration).

Failure to connect with LDAP server

Message: 'TLS or SSL already in effect'

  • You cannot use a ldaps:// URL and a ldap_auth_start_tls set to 1 at the same time. They are mutually exclusive.

GnuTLS error

Message: 'GnuTLS: A TLS packet with unexpected length was received'

  • You may get this error on servers where an old version of the GnuTLS or OpenSSL library was installed.

  • You can change the ciphers used by LDAP libraries with environment variables. For instance:

    export LDAPTLS_CIPHER_SUITE='NORMAL:!VERS-TLS1.2'

SSL certificate error

Message: SSL routines

ssl3_get_server_certificate:certificate verify failed (unable to get local issuer certificate)

  • You can bypass the LDAP certificates verification by using the -N flag.

  • This sets the environment variable LDAPTLS_REQCERT to never

Host/domain error

Message: gss_acquire_cred_impersonate_name: host/domain

name not found'

  • The host name of the server running the SSO agent must resolve to an IP.

  • Add it to your DNS server or in your hosts file.

DNS issues

Message: gss_init_sec_context failed,

major_stat=851968, minor_stat=100006

  • Reverse DNS must work on the server running the SSO agent.

  • You must be able to resolve your server IP to its host name.

  • If not, you can add this /etc/krb.conf, to disable the reverse DNS:

    [libdefaults]
    rdns = false