Shibboleth Service Provider Access Control

Table of contents

Introduction

One of the great advantages of Shibboleth are its capabilities to easily define secure access control rules. Find below many useful examples and explanations of common access control rules and how they can be used effectively.

A resource can be protected with acces rules defined in the web server configuration, in Shibboleth or by the application itself. In all cases a Shibboleth session must be enforced first. This ensures that the user's attributes are available and can be used for access control. A user is then only granted access if his attributes match the defined access control rules.

Unless one implements access control within the application itself by access the AAI attributes, there are three methods how Shibboleth itself can perform access control with Apache or IIS.

Apache: Static configuration
Most web servers are operated with Apache. Shibboleth allows to use Apache directives to protect directories, files or locations in one of Apache's configuration files (e.g. httpd.conf).
The disadvantage of this method is that the web server has to be restarted if an access control rule was changed.
Configuration instructions: Apache Access Rules
Apache: Directory configuration (.htaccess) file
Apache supports the use of so-called .htaccess files, which can overwrite the static configuration if these files are placed in web server directories. The rules defined in this file are dynamicly processed. They are therefore reloaded without restarting the web server. This allows also dynamically changing Shibboleth access rules.
Ensure that the directory that contains an .htaccess file is configured with 'AllowOverride AuthConfig' in the Apache static configuration. This is a prerequisite for Apache to process .htaccess files. file to allow usage of .htaccess files.
The disadvantage of this method is that only existing files and directories can be protected but not arbitrary locations.
Configuration instructions: Apache Access Rules, Combination of .htaccess Files and XML Access Control
IIS/Apache: XML Access rules in Shibboleth configuration
In IIS none of the above-two methods to define Shibboleth access control rules are supported. Therefore, access control rules can only be defined directly in the Shibboleth configuration, either inline or by using a reference to an external file. The inline access rules as well as the externally linked file are loaded dynamically by Shibboleth. Defining access control rules in Shibboleth is also possible with Apache.
Configuration instructions: XML Access Control

Apache Access Rules

Since Apache is the most popular web server in the Internet, let's see how easily access rules can be defined in Apache. A very simple access control rule that could be defined in the Apache configuration looks like this:

# Force user to authenticate on protected-directory
<Location /protected-directory>
  AuthType Shibboleth
  ShibRequestSetting requireSession true
  Require homeOrganizationType university uas
</Location>

This will enforce a Shibboleth session, i.e. users have to authenticate first in order to access the content of the directory "protected-directory" and all its sub directories. The three lines between the <Location> element are the Shibboleth access control directives. The same lines could also be used in an .htaccess file. In this example, the directive Require homeOrganizationType university uas enforces that users must be members of a university or federal institute of technology (homeOrganizationType "university") or a university of applied sciences or university of teacher education (homeOrganizationType "uas").

The directive ShibRequestSetting requireSession true is equivalent to the old directive ShibRequireSession On, which is not recommended to use anymore.

In case the whole Apache web server shall be protected with Shibboleth except for one specific location or sub directory, use the following directives:

# First define a rule to enforce session on all pages
<Location />
  AuthType Shibboleth
  ShibRequestSetting requireSession true
  Require homeOrganizationType university uas
</Location>


# Then list the exceptions
<Location /unprotected>
  AuthType Shibboleth
  ShibRequestSetting requireSession false
  Require Shibboleth
</Location>

If there are multiple Require directives, it's sufficient that any of them matches by default, i.e. they are evaluated as OR conditions. If you want to force that all Require directives must match, i.e. they are evaluated as AND conditions, you need to add the directive ShibRequireAll On. In the following example, a user must be staff member and it's home organization must be uzh.ch.

AuthType Shibboleth
ShibRequestSetting requireSession true
ShibRequireAll On
Require affiliation staff
Require homeOrganization uzh.ch

More information Apache access control directives in general can be found on the pages NativeSPhtaccess and NativeSPApacheConfig of the official Shibboleth Wiki.

Find below additional examples of common access control rules, which are based on an example page by University of Zurich. Also have a look at the AAI Attribute Specification in order to see which attributes one can use in order to create fine-grained access control rules. The attribute names of these access control rules are defined as id (and before SP 2.5 aliases) in the attribute-map.xml of the Shibboleth configuration.

Also have a look at the Expert Home Organisation page for more information about the homeOrg and homeOrgType values of the SWITCHaai Home Organisations.

All users from universities of applied sciences with an AAI login
AuthType Shibboleth
ShibRequestSetting requireSession true
Require homeOrganizationType uas
All users from university of Zurich and ETH Zurich
AuthType Shibboleth
ShibRequestSetting requireSession true
Require homeOrganization uzh.ch ethz.ch
All users from university of Zurich who are staff members
AuthType Shibboleth
ShibRequestSetting requireSession true
ShibRequireAll On
Require affiliation staff
Require homeOrganization uzh.ch
Users whose email address match a regular expression (in this case all D-ITET users from ETHZ)
AuthType Shibboleth
ShibRequestSetting requireSession true
Require mail ~ .*@ee.ethz.ch$
All students from university of Zurich or ETH Zurich
AuthType Shibboleth
ShibRequestSetting requireSession true
ShibRequireAll On
Require affiliation student
Require homeOrganization ~ ^uzh.ch$ ^ethz.ch$
All users from university of Zurich, ETH Zurich or two specific VHO groups
AuthType Shibboleth
ShibRequestSetting requireSession true
Require homeOrganization uzh.ch ethz.ch
Require entitlement ~ ^http://www.olat.uzh.ch/phzh$ ^http://www.olat.uzh.ch/cas_bgm$
Only users with the following e-Mail addresses
AuthType Shibboleth
ShibRequestSetting requireSession true
Require mail ~ ^user-x@switch.ch$ ^user-y@switch.ch$
Only users with the following uniqueIDs
AuthType Shibboleth
ShibRequestSetting requireSession true
Require uniqueID  000123@switch.ch 000455@switch.ch
Only users from a specific VHO group with sub groups
AuthType Shibboleth
ShibRequestSetting requireSession true
Require entitlement ~ ^http://www.olat.uzh.ch/.*$
Only members of a specific Toolbox group
AuthType Shibboleth
ShibRequestSetting requireSession true
Require isMemberOf https://toolbox.switch.ch/mygroup
Only users from Swiss academic education (without library, upper secondary, professional education and training colleges)
AuthType Shibboleth
ShibRequestSetting requireSession true
Require homeOrganizationType university uas hospital others vho
Only Shibboleth users or users from a specific domain/IP range
AllowOverride All

# Use IP Authorisation or Shibboleth Authorisation
Satisfy Any

# IP Authorisation
Order Deny,Allow
Deny from all
Allow from switch.ch
Allow from 130.59.6.143
Allow from 2001:620::4:ca2a:14ff:fe2f:1b97

# Shibboleth Authorisation
AuthType Shibboleth
ShibRequestSetting requireSession true
Require homeOrganization switch.ch

XML Access Control

XML access rules are defined either directly in the Shibboleth configuration file (e.g. shibboleth2.xml within a <Host> element in the <RequestMap>) or in an externally referenced and dynamically loaded XML file.

Note:
In order to use XML access control rules with Apache (e.g. in order to dynamically protect a location), Apache first has to be made aware that Shibboleth shall be active for a given location. This can be achieved by using the configuration directives:

...
# Activate Shibboleth but don't enforce a session
<Location />
    AuthType Shibboleth
    Require Shibboleth
</Location>
...

Inline access control rule
An example of an inline access control rule that protects the directory protected-directory but won't enforce an AAI session on the sub directory unprotected then looks like this:

...
<Host name="sp.example.org">
    <Path name="protected-directory" authType="shibboleth" requireSession="true">
        <AccessControl>
            <AND>
                <Rule require="affiliation">student</Rule>
                <OR>
                    <Rule require="homeOrganization">ethz.ch</Rule>
                    <Rule require="homeOrganization">uzh.ch</Rule>
                </OR>
                <NOT>
                    <Rule require="homeOrganization">vho-switchaai.ch</Rule>
                </NOT>
            </AND>
        </AccessControl>
        <Path name="unprotected" authType="shibboleth" requireSession="false" />
    </Path>
</Host>
...

As can be seen in the example above, the allowed boolean operators are AND, OR and NOT.

Linked access control file
An example of a linked XML access control file is given below. This method has the advantage that changes to the file don't require Shibboleth to be restarted to take effect. The name of the file can be chosen arbitrarily.

...
<Host name="sp.example.org">
  <Path name="secure" authType="shibboleth" requireSession="true">
     <AccessControlProvider uri="/var/www/secure/shibacl.xml"
      type="edu.internet2.middleware.shibboleth.sp.provider.XMLAccessControl"
     />
  </Path>
</Host>
...

The syntax in shibacl.xml looks like (similar to inline but note the required xml namespace definition):

<?xml version="1.0" encoding="UTF-8"?>
<AccessControl xmlns="urn:mace:shibboleth:target:config:1.0">
    <AND>
        <Rule require="affiliation">student</Rule>
        <OR>
            <Rule require="homeOrganization">ethz.ch</Rule>
            <Rule require="homeOrganization">uzh.ch</Rule>
        </OR>
        <NOT>
            <Rule require="homeOrganization">vho-switchaai.ch</Rule>
        </NOT>
    </AND>
</AccessControl>

More information on XML access control can be found on the official SP XML Access Control (Shibboleth Wiki).

Note about Apache, XML based access control and security:
You should set the directive UseCanonicalName On in your Apache configuration (it's off by default), especially if you have configured multiple hostnames in your virtual host in Apache. Else, the configured XML access control rules might be bypassed.

Background: By default, Apache "trusts" the user’s web browser about what the requested hostname is and reports that value internally. Shibboleth chooses the access control rules in a <Host> element based on this hostname. This means that if a virtual host is accessible by multiple hostnames and a browser sends a different hostname than given in the <Host> element, the XML based access control rules might not be applied and thus access control would be bypassed. The directive UseCanonicalName On forces Apache to pass the hostname configured in the directive ServerName to Shibboleth instead of using the hostname sent by the browser.

Please refere to the Shibboleth documentation, "Prepping Apache" for details about this.

Combination of .htaccess Files and XML Access Control

Using .htaccess files has the advantage that access control rules are dynamically processed without restarting the web server. In addition, .htaccess files can be set by any user with write privileges for a web server directory. However, one drawback of .htaccess files is the lack of flexibility when it comes to create access control rules. In comparison to the XML Access Control rules the Apache access control directives can only be connected with boolean OR and AND operators in a very simple way. This may not be sufficient.
But since the Shibboleth Service Provider 2.4 there is a way how the advantages of .htaccess files and XML Access Control rules can be combined. This works using a .htaccess file like:

AuthType Shibboleth
ShibRequestSetting requireSession true
ShibRequireAll On
Require Shibboleth
ShibAccessControl /var/www/aai/shibacl.xml

Add an absolute file path after ShibAccessControl. This file (e.g. /var/www/aai/shibacl.xml) then must contain an XML Access Control rule. For example:

<AccessControl
 type="edu.internet2.middleware.shibboleth.sp.provider.XMLAccessControl">
    <OR>
        <AND>
            <Rule require="homeOrganization">ethz.ch</Rule>
            <Rule require="affiliation">staff</Rule>
            <Rule require="staffCategory">102</Rule>
        </AND>
        <AND>
            <Rule require="affiliation">student</Rule>
            <OR>
                <Rule require="homeOrganization">ethz.ch</Rule>
                <Rule require="homeOrganization">epfl.ch</Rule>
            </OR>
        </AND>
    </OR>
</AccessControl>

This would grant access only to students of ETHZ and EPFL or to lecturers of ETHZ.

Forced re-authentication

For some applications with high security requirements it might be beneficial to break the Single-Sign On feature of AAI and require a reauthentication of the user. This can be achieved by using a SAML2 SessionInitiator with the content parameter forceAuth.
This SAML2 SessionInitiator parameter will force the user to authenticate at the Identity Provider, even if he still has a valid Single-Sign On session. In combination with a Service Provider's logout handler, this feature is especially useful for applications often used at public terminals/kiosks. It allows logged in users to log out from a web application.
To use the forceAuthn parameter, replace the simplified SSO and Logout elements in shibboleth2.xml with:

<SessionInitiator 
    id="Login"
    type="Chaining" 
    Location="/Login" 
    isDefault="true">
    <SessionInitiator 
        type="SAML2" 
        acsByIndex="false" 
        acsIndex="1" 
        template="bindingTemplate.html" 
        forceAuthn="true"/>
    <SessionInitiator 
        type="SAMLDS" 
        URL="https://wayf.switch.ch/SWITCHaai/WAYF"/>
</SessionInitiator>

<md:AssertionConsumerService 
    Location="/SAML2/POST" 
    index="1"
    Binding="urn:oasis:names:tc:SAML:2.0:bindings:HTTP-POST"/>
    
<LogoutInitiator
    type="Local"
    Location="/Logout" />

Attribute Names

If you wonder what the names of the attributes in a web application (e.g. PHP, Perl, ...), they are defined in the file /etc/shibboleth/attribute-map.xml file (the attribute names correspond to the "id=" and "aliases" values of the <Attribute> elements) for Shibboleth 2.x. Alternatively, one can access the Shibboleth session handler after a successful authentication at '/Shibboleth.sso/Session'. This handler also shows the available attributes and their names in the web server environment.

Note:
If the Apache directive 'ShibUseHeaders On' is used as described below, the attributes will not only be available in the web server environment in form of web server environment variables but also in form of HTTP header variables. However, the names of HTTP header variables will be transformed by Apache so that they look differently than defined in the attribute-map.xml file. For instance, the attribute whose 'id' in attribute-map.xml is 'Shib-EP-Entitlement' will be transformed (name in uppercase letters, prepended by 'HTTP_' and all '-' are replaced by '_') to 'HTTP_SHIB_EP_ENTITLEMENT' by Apache.

VHO Users

Remember that users from the Virtual Home Organization can also authenticate via AAI and therefore may access all resource that don't enforce access control rules. In order to prevent VHO users from accessing a service they have to be distinguished from other AAI users. Using a rule like below one can prevent VHO users from accessing protected content:

AuthType Shibboleth
ShibRequestSetting requireSession true
Require homeOrganizationType ~ ^[^vV][^hH][^oO]

or more elegant with an XML Access Control rule:

...
     <NOT>
         <Rule require="homeOrganizationType">vho</Rule>
     </NOT>
...

Alternative Ways to Authorize Users

There are use-cases that involve protecting certain documents, web applications or just certain functions of a web application in a way where only access shall be granted to very specific users of one or more Home Organizations (see graphic below). In such a case, the users that shall get access most probably don't share a common attribute that would allow setting rules like the one above.

Group Management Tool use case

Therefore, it's necessary to set a common attribute for all these users. This can be done using the SWITCHtoolbox, which allows creating groups and subgroups that the can be given access to various tools (wikis, mailing lists, document storage, etc). Adding a tool to the toolbox would allow using a simple access control rule like:

     AuthType Shibboleth
     ShibRequestSetting requireSession true
     Require isMemberOf https://toolbox.switch.ch/phy101
An alternative, would be to collect all uniqueIDs/emails/persistentId values or the users that shall be granted access. This then would allow using an access control rule like:

     AuthType Shibboleth
     ShibRequestSetting requireSession true
     Require uniqueID 234023480@uzh.ch 32489@ethz.ch 435kjsmfsd5@unige.ch [...] 

Although this solution works as assumed, it may be hard to get and maintain all user unique IDs from the people that shall be granted access. The Group Management Tool (GMT) facilitates this process because it allows to easily collect all the uniqueIDs. The GMT is a web application that one has to download and deploy locally.

Java Applications

In case a Java application shall be protected with Shibboleth 2.x and if the applications also shall be able to read Shibboleth attributes, choose one of the following options in order to make Apache forward Shibboleth attributes to the Java application:

  • This is the recommended method.
    If mod_proxy_ajp is used to make Apache forward requests via AJP to a servlet container the following method can be used: In shibboleth2.xml add 'attributePrefix="AJP_"' to the <ApplicationDefaults> (or an appropriate <ApplicationOverride>) element. This is necessary because environment variables are only included in the request by mod_proxy_ajp if they have 'AJP_' prefixes.
    <ApplicationDefaults id="default" policyId="default"
        [...] 
        attributePrefix="AJP_" >
    
  • If mod_jk is used instead of mod_proxy_ajp, configure mod_jk to forward specific environment variables. The Apache configuration directives for accomplishing this are:
            JkEnvVar Shib-Application-ID
            JkEnvVar Shib-Session-ID
            JkEnvVar Shib-Identity-Provider
            JkEnvVar Shib-Authentication-Instant
            JkEnvVar Shib-SwissEP-UniqueID
            JkEnvVar Shib-InetOrgPerson-givenName
            JkEnvVar Shib-Person-surname
    
    This method is not very flexible because each attribute has to be configured explicitly.
  • If for some reason none of the above works, use the old Shibboleth 1.3 behaviour where attributes are stored in the web server environment as header variables. This can be done using an Apache directive called ShibUseHeaders On. This then would look like:
    	AuthType Shibboleth
    	ShibRequestSetting requireSession true
    	ShibUseHeaders On
            Require homeOrganizationType university uas
    
    This option is less secure than the others because headers are easier to spoof in web browsers (particularily IIS).

The underlying reason why one has to adapt the configuration with one of the above options is that Shibboleth attributes are not forwaded to a Java application by default. Shibboleth 2.x in its default configuration doesn't store the attributes as header variables in the web server environment but as environment variables. The effect of this that mod_proxy_ajp and mod_jk won't forward the attributes anymore to the servlet container unless one uses either of the above solutions. More information on this topic can be found on the pages NativeSPhtaccess of the Shibboleth Wiki.

Note: Due to a bug in some servlet containers it may not be possible to read the Shibboleth attributes directly using a loop like:

java.util.Enumeration names = request.getHeaderNames();while (names.hasMoreElements()) {
    String name = (String)names.nextElement();
    out.println(name+": "+request.getHeader(name)+"<br>");
}       

out.print("<br><br><b>Attribute</b><br>");
names = request.getAttributeNames();
while (names.hasMoreElements()) {
    String name = (String)names.nextElement();
    out.println(name+": "+request.getAttribute(name)+"<br>");
}
		

Instead, one has to access the header names directly using something like:

request.getAttribute("Shib-Identity-Provider");

This of course implies that one knows the attribute names. These are defined in the attribute-map.xml as id and aliases of the Attribute elements.