Apache authentication for httpd 2.4

mod_auth_vas4 - Installation


This guide describes how to install Resource Central's mod_auth_vas4 Apache authentication module. Step-by-step instructions are given for an example web server setup on various platforms.

The mod_auth_vas4 module is intended to be compiled from source form for your particular version of Apache HTTPD. This is because the Apache web server's module API changes substantially between different releases and modules compiled for one version of the Apache web server are not guaranteed to function correctly with another. However, Resource Central does provide a few pre-compiled mod_auth_vas4 packages for some of the more popular and stable operating system distributions.

Listed below are the latest releases of mod_auth_vas4, including both binary and source packages:

  NOTE: Packages for Linux distros using Apache have "ap" in their names. Packages for Red Hat's httpd have "http" in their names.

Release: mod_auth_vas4-
Platform Filename Type Size Date MD5 checksum?
Other mod_auth_vas4 releases
linux-x86_64mod-auth-vas-ap24_4.0.2.3-1_amd64.debpackage83 kB2016-02-17674a5f82b5b9ae658361fbe98ccca999
mod-auth-vas-http24- kB2016-02-1729d757ae2dc1373e4f2b5f3d2f114856
sourcemod_auth_vas4- kB2016-02-179ab52ec22858f0d1ab0effb3e5aa3b66

Installing mod_auth_vas4 from source

This section applies to any system where an Apache 2.4 web server, or derivative, is installed.

If you have any issues installing mod_auth_vas4 from source, please take your questions and problems to the web forum so that others may benfit from the solution.

  1. Prerequisites:
    • Quest Authentication Services 3.0 or later
    • the Quest Authentication Services developer kit vasdev (found in the SDK directory on the Authentication Services CD)
    • a C compiler (e.g. gcc)
    • Apache 2.4 or later
    • Your Apache HTTPD's extension tool (look for a program called apxs or apxs2)
    • make. GNU make is necessary to create a platform-native package (such as an RPM). Otherwise any sane version of make will be fine.
  2. Download the source package, mod_auth_vas-[version].tar.gz
  3. Unpack and build the source package:
    $ gzip -dc < mod_auth_vas- | tar fx -
    $ cd mod_auth_vas-
    $ ./configure
    $ make
    If this step fails, please double-check that you have all the required software listed in the earlier steps. You may need to provide the path to apxs explicitly with the --with-apxs option to configure.
  4. If your operating system uses dpkg (deb) or RPM packages, you can build a native package by running:
    $ make package
    The package will be built and put in the pkg directory, then you can install it with the appropriate command, eg. dpkg -i pkg/*.deb or rpm -i pkg/*.rpm . Otherwise install the module directly:
    # make install
  5. Enable the module:

    If you built & installed a package then the module will have been enabled automatically.

    If you installed the module manually you can enable it by adding LoadModule auth_vas4_module /path/to/apache/modules/mod_auth_vas4.so to your Apache config. You can find the module path by running apxs -q LIBEXECDIR . This LoadModule line should be added after the existing LoadModule lines to avoid a possible conflict between the system's libgcc_s.so and Quest Authentication Services' libgcc_s.so.

  6. Run the setup script. This will create the service account in Active Directory and set it up for use with mod_auth_vas4, as well as checking that the local keytab file is usable by the Apache server:
    # /opt/quest/sbin/setup-mod_auth_vas4
    You may need to use the -a and -c options to specify the location of apxs and Apache's config file. Run /opt/quest/sbin/setup-mod_auth_vas4 -h for details. It is safe to run setup-mod_auth_vas4 more than once, for example to review the state of the service account.
  7. Restart the Apache server. (Usually /etc/init.d/httpd restart or /etc/init.d/apache2 restart)

As the source is available, you are free to modify and enhance the module. If you extend mod_auth_vas4 in a way that is likely to be useful to other Quest Authentication Services users, please share the changes with us! Contact the web forum and we can add it to future distributions with credit.

Compiling issues

A common compile issue when building MAV is mod_auth_vas4.c:48:25: error: gssapi_krb5.h: No such file or directory This can be fixed by adding CPPFLAGS=-I/opt/quest/bin/gssapi to end of your configure line.

Compiling for Oracle HTTP Server

When running the configure script, it is likely that the compiler reported by apxs will not work. In that case, re-run ./configure with CC=gcc at the end of the command-line to override the choice of compiler:

$ ./configure CC=gcc

If you get an error that strict.pm is not found when running apxs, consider changing the apxs script (Apache/Apache/bin/apxs) to use the system's perl instead of Oracle's bundled perl by changing the first line of the apxs script to

(or wherever your system's perl program is).

If you get an error loading libdms2.so when starting httpd, set the LD_LIBRARY_PATH environment variable to your ORACLE_HOME/lib directory.

Installing on a server that is not joined to the domain

Running on a server that is not joined to the same domain is not a supported configuration for mod_auth_vas4. mod_auth_vas4 is designed to work on a machine that is joined to the same domain, however many configurations (such as a simple "Require valid-user") usually do work on a machine that is joined to another, untrusted domain or not joined at all. If it does work you might find that some operations are slow or cause more network traffic than when run on a server that is joined to the same domain.

To install mod_auth_vas4 on a machine that is not joined to the domain, the domain must be set in /etc/opt/quest/vas/vas.conf by adding a line in the "[libdefaults]" section like so:

  default_realm = EXAMPLE.COM

This should be done before executing the setup-mod_auth_vas4 script. All other installation steps are the same, including the requirement of having the Quest Authentication Services package(s) installed.

Configuring mod_auth_vas4

After installing mod_auth_vas4, you now need to configure the web server to enable it for authentication and authorization on the resources you want protected. The next sections detail this process.

Per-server configuration

mod_auth_vas4 understands the following directives when they are used in the httpd.conf file's global and/or <VirtualHost> sections.

AuthVasApiDebugLevel level

Debug verbosity levels for the Authentication Services API logging. Debug will be written out to system log under the name mod_auth_vas4. Debug levels 0-6. Debug level 3 or higher will include nested logging when an error occurs from the LDAP or KRB5 layers of the API. The default is level 0. (Since mod_auth_vas

AuthVasCacheSize size

The number of user objects to keep in mod_auth_vas's user cache. The default is 200. (Since mod_auth_vas 3.6.0)

AuthVasCacheExpire time

The amount of time (in seconds) after which cached user objects shall be expired from mod_auth_vas's user cache. The default is 60 seconds. (Since mod_auth_vas 3.6.0)

AuthVasNegGroupCacheSize size

The number of user objects to keep in mod_auth_vas's negative group cache. The default is 200. (Since mod_auth_vas

AuthVasNegGroupCacheExpire time

The amount of time (in seconds) after which cached invalid group objects shall be expired from mod_auth_vas's negative group cache. The default is 60 seconds. (Since mod_auth_vas

AuthVasDefaultRealm realm

Changes the default Active Directory domain to assume when matching usernames with Require user. The domain defaults to the realm to which the host is joined. The domain is also displayed to users when Basic authentication is being used. Defaults to the domain that Quest Authentication Services is currently using to join the web server host to Active Directory.
Note: An Active Directory 'domain' is the same as a Kerberos 'realm', and is usually written in uppercase, e.g EXAMPLE.COM. Active Directory domains should not be confused with DNS domains, although they're usually closely related.

AuthVasKeytabFile path

The keytab file containing the server's Kerberos credentials. If not set, it is automatically derived from the AuthVasServerPrincipal — usually /etc/opt/quest/vas/HTTP.keytab. (Since mod_auth_vas 3.6.0)

AuthVasServerPrincipal principal

Changes the user principal name (LDAP userPrincipalName) used by the web server. Defaults to HTTP/ which Quest Authentication Services expands to HTTP/hostname@realm, where hostname is the local machine's fully-qualified domain name, and realm is the realm (or domain) to which the host is joined. Normally this directive is not needed. (Since mod_auth_vas 3.6.0)

A HTTP/ service key is necessary for your web server to engage in an SPNEGO exchange. The secret key is kept in two places: in a file accessible to the web server and in a host-based service account object inside the Active Directory server. The easiest way to create the service account and key is to use the setup-mod_auth_vas4 command on the web server:

# /opt/quest/sbin/setup-mod_auth_vas4

Alternatively you can invoke vastool manually:

# vastool service create HTTP/

The above command creates the file /etc/opt/quest/vas/HTTP.keytab, which you should immediately chmod or chown so that the Apache web server can read it. The recommended permissions on the file are such that only the web server group can read it:

-rw-r----- 1 root apache 5600 Oct  4 09:28 /etc/opt/quest/vas/HTTP.keytab

Per-directory configuration

The following directives can be placed in a .htaccess file, or in a <Directory> or <Location> section within httpd.conf.

AuthType VAS4

Enables the mod_auth_vas4 module as a type of user authentication during requests on the resource.

It permits the module to deny access to the resource depending on the satisfaction of the Require directives. See also the Apache 2.4 documentation on AuthType

AuthVasProvider provider-name [provider-name] ...

Sets which provider is used to authenticate the user. Any provider that supports password authentication can be used, such as file and digest.
If AuthVasProvider is not set or no provider is listed the default provider is vas4.


<Location /secure> 
    AuthType VAS4 
    AuthVasProvider file vas4 
    AuthUserFile /www/etc/basicauth 
    Require valid-user
Each provider is asked in order until a provider returns a match for the user. When a match for the username is found the responding provider will attempt to check the users password. If the provider is not able to validate the users password, authentication will fail and the password check does not get passed onto the remaining providers.

This directive works the same as AuthBasicProvider. See also Apache's documentation on AuthBasicProvider. (Since mod_auth_vas 4.0.0)

AuthName string

Optional string to be used in Basic authentication prompts. If not set, the Kerberos realm will be used instead. See also Apache's documentation on AuthName.

AuthVasAuthoritative [On|Off]

If this option is turned Off, mod_auth_vas4 will perform authorization checks but instead of immediately denying an unauthorized user, other configured authorization modules will be tried.

This option only affects what happens when a user is not authorized. If a user is authorized by mod_auth_vas4 then they will always be allowed access. The default is On.

default (both on) AuthVasAuthoritative Off AuthVasAuthz Off
Do mod_auth_vas4 authorization checks? yes yes no
Try other modules if authorization fails? no yes yes

See also AuthVasAuthz and Apache's documentation on Authentication, Authorization and Access Control.

AuthVasAuthz [On|Off]

Can be set Off to disable mod_auth_vas4 authorization checks. This might be useful if you want to use both Negotiate (SSO) and Basic (password) authentication, but you want to use another module to do all the authorization checks. For instance this can be used with mod_authz_svn which also has a "Require valid-user" option that bases its authorization decisions on the contents of its AuthzSVNAccessFile. The default is On, meaning mod_auth_vas4 will provide authorization checks.

See also AuthVasAuthoritative and Apache's documentation on Authentication, Authorization and Access Control. (Since mod_auth_vas 3.6.0).

AuthVasExportDelegated [On|Off]
Stores delegated credentials in a temporary credential cache file on each request. The default setting is Off. The path to the file is supplied in the KRB5CCNAME environment variable. Note that the created file is owned by the web server user and may be inaccessible when SUEXEC is active. It is deleted when the request completes.
AuthVasNTLMErrorDocument [ default | message | document ]
mod_auth_vas4 provides a built-in error page to clients that try NTLM authentication. The error page contains some hints on browser configuration. It can be overridden in a per-directory context in a similar way to Apache's ErrorDocument option, namely by specifying a custom error message or URL. For example:
AuthVasNTLMErrorDocument default
AuthVasNTLMErrorDocument "NTLM not supported" 
AuthVasNTLMErrorDocument /errors/ntlm.html
We recommend configuring your own site-specific document that covers the most likely solutions for your users. Don't forget to make the error page accessible by unauthenticated users. Use a <Files> container with Satisfy any to make exceptions, or store it in an unprotected directory. (Since mod_auth_vas 3.5.0)
AuthVasRemoteUserMap [ default | local | ldap-attr attr ]
Determines how the REMOTE_USER variable should be set. The parameter has the following meaning
  • default: the user's Kerberos principal name (sAMAccountName@REALM, eg. john@EXAMPLE.COM)
  • local: A local representation of the user. This means the canonical local username if they belong to the same realm, or the user's full Kerberos principal name for cross-realm users. All authenticated users regardless of Unix-enablement will be localized in this manner.
  • ldap-attr attr: Any LDAP attribute fetched from the authenticated user's Active Directory user object. The following attributes are usually resolved from the Quest Authentication Services cache and do not cause LDAP traffic:
    • userPrincipalName
    • sAMAccountName
    • distinguishedName
    • objectSid
    • uidNumber
    • gidNumber
    Other LDAP attributes will cause LDAP traffic for each request.
(Since mod_auth_vas 3.5.0)
AuthVasSuexecAsRemoteUser [On|Off]
Configures mod_suexec to execute CGI scripts as the remote authenticated user. This option overrides mod_suexec's SuexecUserGroup directive (which can only be specified per-server and not per-directory). If mod_suexec is not loaded, this option has no effect.
The default setting is Off.
This option was added in mod_auth_vas 3.5.0. Prior to that, mod_auth_vas behaved as if this option was On.
AuthVasUseBasic [On|Off]
Enables/disables use of the Basic authentication fallback when the web browser/client does not understand the reply header WWW-Authenticate: Negotiate. When enabled, a second reply header is sent to the client: WWW-Authenticate: basic. This is sufficient for some browsers to prompt the user for their login name and password, and retry using Basic authentication. If the web server is not using SSL (HTTPS), then the user's password will be visible on the network. This configuration inherits its settings from parent directories. The initial setting is Off.
AuthVasUseNegotiate [ On | Off | subnet... ]
Enables/disables use of Negotiate authentication (SPNEGO). This configuration inherits its settings from parent directories. The initial setting is On.
Negotiate authentication can be enabled on a subnet-specific basis by specifying a list of subnets instead of On or Off. Subnets are specified in the network/mask notation. The optional /mask can be an IP address or the number-of-bits (CIDR notation). If left out, the mask is assumed to be /32 for IPv4 or /128 for IPv6, that is, exact IP address matching is performed. Multiple subnets may be specified, separated by spaces. Examples of directive use:
AuthVasUseNegotiate On
AuthVasUseNegotiate Off
Examples of valid subnet expressions (IPv6 only available on Apache 2):
The AuthVasUseNegotiate option can be used on machines that serve both internal (Kerberos-capable) and external clients. It can prevent the external Internet Explorer clients erroneously trying to use NTLM authentication. See bug 337.
Support for subnet-specific Negotiation was added in mod_auth_vas 3.5.0. Prior to that it could only be On or Off.
Require user upn...
Causes the authorization phase to succeed if the authenticated user principal name matches any of the given user principal names. An example of a user principal name is john@EXAMPLE.COM. Each upn may also be a simple username, in which case the default realm (see AuthVasDefaultRealm) will be automatically appended.

Can also use usernames that are found in the AuthUserFile when file is listed as one of the providers in AuthVasProvider. See Apache's 2.4 documentation on AuthUserFile.

Require group group...
Causes the authorization phase to succeed if the authenticated user is a member of any of the groups named in the AuthGroupFile. Group names containing spaces should be quoted with double quotes, and should match the format provided by AuthVasRemoteUserMap.

See Apache's 2.4 documentation on AuthGroupFile.

Require unix-group group...
Causes the authorization phase to succeed if the authenticated user is a member of any the listed unix groups. Unix groups can consist of both local unix groups and Active Directory Unix enabled groups.

unix-group is a VAS4 AuthType specific authorization provider. (Since mod_auth_vas 3.3.0)

Require ad-group Active Directory group...
Causes the authorization phase to succeed if the authenticated user is a member of any of the Active Directory groups named. Group names containing spaces should be quoted with double quotes.

ad-group is a VAS4 AuthType specific authorization provider. (Since mod_auth_vas 4.0.0)

Require ad-dn dn...
Causes the authorization phase to succeed if the authenticated user is within any of the given Active Directory containers named by the distinguished name dn. Normally, these are organizational unit names expressed as X.500 distinguished names.

ad-dn is a VAS4 AuthType specific authorization provider. (Since mod_auth_vas 4.0.0)

For example:
Require ad-dn "cn=Employees, dc=example, dc=com"
Require valid-user
Causes the authorization phase to succeed if the user was authenticated. Any user that can obtain a ticket for the web service will satisfy this requirement. This allows you to trust all forests and domains that share some kind of trust relationship with the Active Directory server with which your web server host has joined.

See also: AuthType, Require, AuthAuthoritative

Configuring for virtual hosts

It is common to have a single Apache HTTP server serving multiple different sites for different hostnames. It is called virtual hosting and mod_auth_vas4 is capable of providing access control for virtual hosts.

Setting up a virtual host

There are several steps involved in setting up a virtual host to use mod_auth_vas4 for single sign-on. The following example assumes a web server with the hostname server123.example.com and with a DNS CNAME alias www.example.com. Clients will either access the site as http://server123.example.com/ or as http://www.example.com/. The server only needs to know that it is called server123.example.com, so long as there are servicePrincipalName entries in LDAP matching the names clients will use to access the server.

1. Make sure the HTTP/ service has been created. The simplest way is to run

# /opt/quest/sbin/setup-mod_auth_vas4
as root. The setup-mod_auth_vas4 script will handle creation of the HTTP/ service account in Active Directory and the local keytab. You can add SPN aliases when running the script.

You could also manually create the service account using the vastool service create command. See the vastool manual page for more information.

Once you have created the HTTP/ service account, check what SPNs are attached to it by using vastool attrs:

$ vastool attrs -s HTTP/server123.example.com servicePrincipalName
servicePrincipalName: HTTP/server123.example.com

A newly-created service will have just one SPN. Keep a record of the existing servicePrincipalName values for the next step.

2. Add more servicePrincipalName attribute values using the vastool setattrs command. You must specify the existing servicePrincipalName values on the command line, otherwise they will be replaced. For example:

$ vastool attrs -s HTTP/server123.example.com servicePrincipalName
servicePrincipalName: HTTP/server123.example.com
$ vastool setattrs -sm HTTP/server123.example.com servicePrincipalName \
  HTTP/server123.example.com HTTP/www.example.com
Attribute changed: servicePrincipalName

Check that the new SPNs have been correctly updated:

$ vastool attrs -s HTTP/server123.example.com servicePrincipalName
servicePrincipalName: HTTP/www.example.com
servicePrincipalName: HTTP/server123.example.com

Quest Authentication Services, and earlier only: current versions of Quest Authentication Services use implicit aliasing when matching entries in the keytab, making this step unnecessary.

3. Set up the alias in the local keytab file. Unlike vastool setattrs, you do not need to specify existing alias when creating keytab aliases:

# vastool ktutil -k /etc/opt/quest/vas/HTTP.keytab \
  alias HTTP/server123.example.com HTTP/www.example.com

Confirm the alias has been added:

# vastool ktutil -k /etc/opt/quest/vas/HTTP.keytab list

Vno  Type              Principal
  2  arcfour-hmac-md5  server123-HTTP@EXAMPLE.COM
  2  arcfour-hmac-md5  HTTP/server123.example.com@EXAMPLE.COM
  2  arcfour-hmac-md5  HTTP/www.example.com@EXAMPLE.COM

4. Adjust the Apache configuration files as necessary. This means adding AuthType VAS4 to enable mod_auth_vas4 for that <VirtualHost>, and setting access controls with Require directives. mod_auth_vas4 determines the ServerPrincipalName to use automatically based on the ServerName, which is usually correct. This can be overridden with mod_auth_vas4's AuthVasServerPrincipal option. The AuthVasDefaultRealm option is also useful for cross-domain environments.

<VirtualHost *:80>
    ServerName www.example.com
    AuthVasServerPrincipal HTTP/server123.example.com@EXAMPLE.COM
    AuthVasDefaultRealm EXAMPLE.COM

Virtual host troubleshooting tips

Example configuration files

Here is a simple .htaccess that authenticates everyone except anonymous users:

AuthType VAS4
Require valid-user

Here is a more complicated example .htaccess:

AuthType VAS4
Require user alice bob alice@ELSEWHERE.COM
Require unix-group finance
Require unix-group it
Require ad-group "Domain Admins"
Require ad-dn "ou=Sales, dc=example, dc=com"

AuthVasUseBasic on
If the server is joined to the EXAMPLE.COM domain, then the directives above allow the following users to access files in the directory:

The last line (AuthVasUseBasic on) enables the insecure 'Basic' authentication fallback, and should only be used with HTTPS.

Here are example fragments for httpd.conf:

AuthVasDefaultRealm EXAMPLE2.COM
<Directory "/srv/www/mytestdir">
    AllowOverride All
    AuthType VAS4
<VirtualHost *:80>
    ServerName www.example.com
    AuthVasDefaultRealm EXAMPLE.COM
    AuthVasServerPrincipal HTTP/www.example.com@EXAMPLE.COM

The first line changes the default realm, used by the Require user directive. The <VirtualHost> section gives an example of how different service keys can be used.

Known limitations

The following are known limitations with mod_auth_vas4:

See also: the troubleshooting guide, or the product bug tracker.

- David Leonard
- Updated for MAV4 - Jayson Hurst