Zope 2/Plone extension for SAML2 based Single Sign On: identity, attribute and service providers
This package supports SAML2 based SSO (Single Sign-On) for Zope2/Plone installations.
While it currently supports only a small subset of the SAML2 standard (simple identity provider, simple service provider integration and attribute support), its current functionality is comparable to Plone’s OpenId support.
In the SAML2 architecture, a set of distributed authorities (aka entities) cooperate to provide an overall service. Each authority can take over one or more roles. Roles are for example “identity provider” (can identify users), “service provider” (provides some service) and “attribute provider” (can provide information about users). Authorities and their roles are described by metadata. The metadata is exchanged between authorities to allow them to cooperate. SAML2 messages are exchanged to implement the SSO (and other) functionality.
The package currently provides an SAML2 authority, a simple identity provider, a simple service provider integration and a simple attribute provider. All functions are implemented via objects created via the Zope management interface (ZMI).
In general, an identity provider has the task to identify users and to provide assertions about user identities to service providers.
The provided simple identity provider delegates the first task (identifying users) to a host CMF or Plone portal. Thereby, it uses the standard portal functionality for login and authentication; it does not make any assumption about the way the portal manages its users (and their attributes) and the details of the authentication process. Thus, almost any portal can be made into an SAML2 identity provider by just creating an “Saml simple identity provider” in the portal.
On creation, the identity provider registers automatically as “identity provider” role with an SAML authority utility. Creation fails, if this utility either cannot be located or already knows about an identity provider.
There is a variant identity provider which integrates elemantary attribute provider functionality (see section “Attribute Support”).
In general, an SAML2 service provider provides some kind of (web) service to users and uses SAML2 to get information about the identities, attributes or access rights for some of its users. The service provided itself has nothing to do with SAML2; it can be almost anything (using web technologies). Only a small part has to do with SAML2: getting information about users identified and managed externally by other SAML2 authorities.
The simple service provider functionality in this package allows either a single portal or a family of portals sharing a common service provider description to get authentication information from an SAML2 identity provider. It interfaces with the portal[s] via the miniframework “pluggable authentication service”, used by (e.g.) Plone portals.
In the simple case, the (real) service is implemented by a single portal which should get authentication information from one or more SAML2 identity providers. This use case is supported by the creation of an “Saml integrated simple spsso plugin” in the portal’s acl_users and the activation of its interfaces.
If the SAML2 based authentication replaces the local one, plugins responsible for local authentication may need to be removed or their interfaces deactivated. Some integration work is necessary, when local authentication should coexist with SAML2 based authentication (essentially, the login form (for local authentication) must be combined with the identity provider selection (for external authentication)).
In the more complex case, the (real) service is not provided by a single portal but by a whole family of portals (usually providing the same service or slightly customized variants of the same service to different user groups) sharing a common service description with respect to SAML2. In this case, there is a shared Saml service provider and each portal has an Saml simple spsso plugin (external spsso) which work with the shared service provider. In this case, service provider and plugin communicate via cookies. Therefore, they must get the same cookies.
In fact, the simple case is a variant of the complex one where service provider and plugin are implemented by the same object.
When a service provider object is created (either standalone or integrated with the plugin), it registers as “service provider” role with an SAML authority utility. Creation fails, if this utility either cannot be located or already knows about a service provider.
The servide provider integration can exhibit user attributes from the SAML2 assertions as user properties in the portal (user properties are a standard feature of Plone portals – to provide addtional information such as name, email address, … for a user).
General SAML2 Attribute Support
This section sketches the general principles of SAML2 attribute support. The next section outlines the support provided by this package.
The SAML2 assertions about a user can include almost arbitrary attributes to provide additional information (beyond the identity). Attributes can for example be used to inform a cooperating SAML authority about the name, the email address, group membership or special priviledges of a user.
SAML2 attributes are identified by a name format and a (formal, often unwieldy) name. Optionally, they can have a so called “FriendlyName” which should be human readable.
SAML2 allows a service provider to define zero or more “AttributeConsumingService”s. Each “AttributeConsumingService” is identified by an index (an integer) and contains a sequence of descriptions for “RequestedAttribute”s. When the service provider requests authentication for a user, it can specify for which of its “AttributeConsumingService”s it wants attribute information.
An SAML2 attribute provider is able to provide attributes for users. Metadata tells which attributes can be provided.
Attribute Support in this Package
This package describes attributes by objects, managed in “Folder”s and identified by (locally unique) ids. The ids are used as “FriendlyName” in the SAML metadata and as user property name. The attribute’s SAML2 name format and (formal) name are specified by attributes of the attribute (describing) object.
Attribute values can be instances of an XML-Schema elementary type or lists/sequences thereof (however, Plone may not understand some of those types).
The service provider object is implemented as a “Folder” of “AttributeConsumingService”s, each “AttributConsumingService” as a “Folder” of “RequestedAttribute”s. Thus, a service provider can define various sets of interesting attributes. However, the standard authentication request requests only the default set. While there is an authentication method which supports the specification of the wanted “AttributeConsumingService”, it is likely that this in not yet handled correctly in this version.
The service provider plugin exposes the SAML2 attributes for a user as standard (for Plone) user properties; the id of the attribute description is used as user property name.
The current package version does not have a standalone attribute provider. However, there is an identity provider variant which has some integrated attribute provider functionality. It provides attribute information only as part of authentication requests. It is implemented as a “Folder” of “Attribute”s which describe the supported attributes and how their value can be computed. By default, the id of the attribute description is interpreted as user property name and its value (for the current user) used as value for the attribute. Alternatively, the attribute definition can specify an “Evaluator” – the name of a method or view called with parameters member, attr and eid to determine the attribute value. member is the current portal member, attr the attribute description and eid the entity identifier who should get the information.
The package depends on Zope2. It was tested both with Zope 2.10 and Zope 2.13 (therefore, it is expected to work with the intermediate versions as well). For Zope versions from 2.12 onward, you must ensure that five.formlib is installed (as Zope 2.12 dropped zope.formlib support from the core; it was moved into a the separate package five.formlib).
Note that one of the dependencies (pyxb in version 1.1.4) has problems to get installed via package managers with Python versions before 2.6. This makes some problems with Zope 2.10 and 2.11. Consult the dependecies section of dm.saml2 to learn how you can work around this problem.
You must install the code for the package and ensure that the package’s ZCML definitions are interpreted on Zope startup. In addition, you must ensure that on Zope startup, the xmlsec library is initialized (by calling dm.xmlsec.binding.initialize()).
In order to learn details about xmlsec signing/verification failures, you might want to use dm.xmlsec.binding.set_error_callback to let those details be logged (for details, consult the dm.xmlsec.binding documentation).
In the case that you are using zc.buildout for your Zope2 installation, then the installation steps can be summarized as follows:
- extend the eggs definition in your buildout.cfg by dm.zope.saml2 and (in case you are using Zope2 >= 2.12) by five.formlib.
- extend the zcml definition in your buildout.cfg by dm.zope.saml2.
- ensure dm.xmlsec.binding.initialize() gets called on Zope startup.
The default zope.formlib support for Password fields is very bad (it carefully hides the password on edits but displays it in clear text on views; it forces you to reenter the password anew whenever you save the form). To get decent handling of Password fields, you may want to activate the ZCML overrides of package dm.zope.schema. If you are using zc.buildout. you can achieve this by extending the zcml definition in your buildout.cfg by dm.zope.schema-overrides.
SAML2 stives hard for security. Therefore, it is virtually impossible to use SAML2 in an identify provider without digital signatures. The digital signatures are used to prevent tempering with SAML2 messages and to authenticate the cooperationg SAML2 authorities. To effectively use SAML2 for an identity provider, you will need a certificate and an associated private key such that the authentication assertions can be properly signed. A certificate can be obtained from a standard CA (certificate authority); certificates used for HTTPS servers are usable. Alternatively, it may be possible (this depends on the SAML2 partners, you want to cooperate with) to generate your own certificate. “http://www.imacat.idv.tw/tech/sslcerts.html” describes how you can do this on a Unix-like platform. Private key and certificate are specified when you create an SAML authority. For service providers (in contrast to identity providers) a certificate may not be necessary (this depends on the identity providers you want to cooperate with; if they (all) accept unsigned authentication requests, a private key/certificate pair is not necessary).
In case, the interaction between SAML entities poses problems, the logging facility of dm.zope.saml2 can be helpful. Logging is enabled by setting the envvar SAML2_ENABLE_LOGGING to a non empty value. It causes all incoming and outgoing SAML messages to be logged on level INFO.
The package supports several levels of customizations: basic customizations via the ZMI through configuration menues, customization by registration of adapters and integrating your own class implementations, possibly derived from base classes defined in this package.
When you create objects described in the architecture section, you are sent to a configuration menue to enter the relevant configuration parameters. Those menues should be self explanatory.
Via the registration of appropriate adapters, you can currently control the supported nameid formats, the storage used by the RelayStateManager and the generation of urls for role objects. The relevant adapter interfaces are defined in dm.zope.saml2.interfaces.
The built in nameid format support supports only the unspecified format. Via the registration of an INameidFormatSupport role adapter, you can control which nameid formats the adapted role should support.
By default, the RelayManagerState (used to remember state during the login process) is stored inside the ZODB in a role attribute. By defining an IRelayStateStore role adapter you can provide a different store. Note that this adaptation takes effect only during the creation of the role. Should you plan to switch storage at a later time, you must call Sso.__init__ on the role again. Note that aborted login processes leave state records behind. To get rid of them, consider to call the role’s clear method from time to time (maybe once in a month).
The generation of the role urls used in the metadata is a bit complex. The first reason is of a technical nature: the generation may be activated in a context where the request object cannot be accessed in the normal Zope way (i.e. via acquisition); therefore, the normal methods to determine an url do not work (reliably). The second reason comes from the fact that a Zope installation can often be accessed via different urls (e.g. an internal one and one via a virtual host and that the metadata is cached; the cached urls in the metadata must ensure they are valid for all cases and therefore must not depend on the specific request url that accidentally lead to their creation. To work around this complexity, the default behavior is to generate the role urls from a base url (specified as authority configuration attribute) and the path to the respective role. This usually generates valid urls but they are often longer than necessary and may reveal details of the internal structure of your Zope installation (the full path to the role objects) which you might want to hide. For those cases, you can register an authority IUrlCustomizer adapter and there determine the role urls you would like.
For all cases for which the provided customization possibilities are not sufficient, you can define your own classes and instantiate them in place of the standard ones.
I have developed this package as part of a (paid) project - by factoring out into this open source package the parts which might be useful to others. However, I did not invest much effort towards things not relevant to my project. Especially, I have not performed extensive interoperability tests.
The package works for my project and it should work with SimpleSAMLphp (http://simplesamlphp.org/) which I used as functional blueprint. Should I detect interoperability problems in future projects of mine, I will investigate and fix them.
When you use this package in your own projects, you might hit interoperability problems. In those cases, you will need to investigate (and potentially fix them) or use another SAML integration. You may send me your fixes and I will consider whether to incorporate them in future versions.
2.0b3 - 2.0b8
Various fixes and improvements based on experience by Dylan Jay
Improves control over name identifier formats and the creation of name identifiers.
Adds titles to entities in order to provide a more friendly identity provider list.
Ignores signatures in metadata to avoid a chicken-and-egg problem (but this, of course, reduces security).
Supports authentication request signing (if the identity provider requires this).
Version 2.0 uses dm.xmlsec.binding as Python binding to the XML security library, rather then the no longer maintained pyxmlsec. This drastically facilitates installation.
Initial release based on pyxmlsec.