FEDERATED IDENTITY MANAGEMENT
Federated identity management is a relatively new concept dealing with the use of a common identity management scheme across multiple enterprises and numerous applications and supporting many thousands, even millions, of users. We begin our overview with a discussion of the concept of identity management and then examine federated identity management.
Identity management is a centralized, automated approach to provide enterprise- wide access to resources by employees and other authorized individuals. The focus of identity management is defining an identity for each user (human or process), associating attributes with the identity, and enforcing a means by which a user can verify identity. The central concept of an identity management system is the use of single sign-on (SSO). SSO enables a user to access all network resources after a sin- gle authentication.
[PELT07] lists the following as the principal elements of an identity manage- ment system.
• Authentication: Confirmation that a user corresponds to the user name provided.
• Authorization: Granting access to specific services and/or resources based on the authentication.
• Accounting: A process for logging access and authorization.
• Provisioning: The enrollment of users in the system.
• Workflow automation: Movement of data in a business process.
• Delegated administration: The use of role-based access control to grant permissions.
• Password synchronization: Creating a process for single sign-on (SSO) or reduced sign-on (RSO). Single sign-on enables a user to access all network resources after a single authentication. RSO may involve multiple sign-ons but requires less user effort than if each resource and service maintained its own authentication facility.
• Self-service password reset: Enables the user to modify his or her password.
• Federation: A process where authentication and permission will be passed on from one system to another—usually across multiple enterprises, thereby reducing the number of authentications needed by the user.
Note that Kerberos contains a number of the elements of an identity manage- ment system.
Figure 15.3 [LINN06] illustrates entities and data flows in a generic identity management architecture. A principal is an identity holder. Typically, this is a human
user that seeks access to resources and services on the network. User devices, agent processes, and server systems may also function as principals. Principals authenticate themselves to an identity provider. The identity provider associates authentication information with a principal, as well as attributes and one or more identifiers.
Increasingly, digital identities incorporate attributes other than simply an identi- fier and authentication information (such as passwords and biometric information). An attribute service manages the creation and maintenance of such attributes. For example, a user needs to provide a shipping address each time an order is placed at a new Web merchant, and this information needs to be revised when the user moves. Identity management enables the user to provide this information once, so that it is maintained in a single place and released to data consumers in accordance with autho- rization and privacy policies. Users may create some of the attributes to be associated with their digital identity, such as an address. Administrators may also assign attrib- utes to users, such as roles, access permissions, and employee information.
Data consumers are entities that obtain and employ data maintained and provided by identity and attribute providers, which are often used to support autho- rization decisions and to collect audit information. For example, a database server or file server is a data consumer that needs a client’s credentials so as to know what access to provide to that client.
Identity federation is, in essence, an extension of identity management to multiple security domains. Such domains include autonomous internal business units, exter- nal business partners, and other third-party applications and services. The goal is to provide the sharing of digital identities so that a user can be authenticated a single time and then access applications and resources across multiple domains. Because these domains are relatively autonomous or independent, no centralized control is possible. Rather, the cooperating organizations must form a federation based on agreed standards and mutual levels of trust to securely share digital identities.
Federated identity management refers to the agreements, standards, and tech- nologies that enable the portability of identities, identity attributes, and entitlements across multiple enterprises and numerous applications and supporting many thou- sands, even millions, of users. When multiple organizations implement interoperable federated identity schemes, an employee in one organization can use a single sign- on to access services across the federation with trust relationships associated with the identity. For example, an employee may log onto her corporate intranet and be authenticated to perform authorized functions and access authorized services on that intranet. The employee could then access their health benefits from an outside health-care provider without having to reauthenticate.
Beyond SSO, federated identity management provides other capabilities. One is a standardized means of representing attributes. Increasingly, digital identities incorporate attributes other than simply an identifier and authentication informa- tion (such as passwords and biometric information). Examples of attributes include account numbers, organizational roles, physical location, and file ownership. A user may have multiple identifiers; for example, each identifier may be associated with a unique role with its own access permissions.
Another key function of federated identity management is identity mapping. Different security domains may represent identities and attributes differently. Further, the amount of information associated with an individual in one domain may be more than is necessary in another domain. The federated identity manage- ment protocols map identities and attributes of a user in one domain to the require- ments of another domain.
Figure 15.4 illustrates entities and data flows in a generic federated identity management architecture.
The identity provider acquires attribute information through dialogue and pro- tocol exchanges with users and administrators. For example, a user needs to provide a shipping address each time an order is placed at a new Web merchant, and this information needs to be revised when the user moves. Identity management enables the user to provide this information once, so that it is maintained in a single place and released to data consumers in accordance with authorization and privacy policies.
Service providers are entities that obtain and employ data maintained and provided by identity providers, often to support authorization decisions and to collect audit information. For example, a database server or file server is a data consumer that needs a client’s credentials so as to know what access to provide to
that client. A service provider can be in the same domain as the user and the identity provider. The power of this approach is for federated identity management, in which the service provider is in a different domain (e.g., a vendor or supplier network).
STANDARDS Federated identity management uses a number of standards as the building blocks for secure identity exchange across different domains or hetero- geneous systems. In essence, organizations issue some form of security tickets for their users that can be processed by cooperating partners. Identity federation standards are thus concerned with defining these tickets, in terms of content and format, providing protocols for exchanging tickets and performing a number of management tasks. These tasks include configuring systems to perform attribute transfers and identity mapping, and performing logging and auditing functions.
The principal underlying standard for federated identity is the Security Assertion Markup Language (SAML), which defines the exchange of security infor- mation between online business partners. SAML conveys authentication informa- tion in the form of assertions about subjects. Assertions are statements about the subject issued by an authoritative entity.
SAML is part of a broader collection of standards being issued by OASIS (Organization for the Advancement of Structured Information Standards) for feder- ated identity management. For example, WS-Federation enables browser-based federation; it relies on a security token service to broker trust of identities, attributes, and authentication between participating Web services.
The challenge with federated identity management is to integrate multiple technologies, standards, and services to provide a secure, user-friendly utility. The key, as in most areas of security and networking, is the reliance on a few mature standards widely accepted by industry. Federated identity management seems to have reached this level of maturity.
EXAMPLES To get some feel for the functionality of identity federation, we look at three scenarios, taken from [COMP06].
In the first scenario (Figure 15.5a), Workplace.com contracts with Health.com to provide employee health benefits. An employee uses a Web interface to sign on to Workplace.com and goes through an authentication procedure there. This enables the employee to access authorized services and resources at Workplace.com. When the employee clicks on a link to access health benefits, her browser is redirected to Health.com. At the same time, the Workplace.com software passes the user’s identi- fier to Health.com in a secure manner. The two organizations are part of a federation that cooperatively exchanges user identifiers. Health.com maintains user identities for every employee at Workplace.com and associates with each identity health- benefits information and access rights. In this example, the linkage between the two companies is based on account information and user participation is browser based.
Figure 15.5b shows a second type of browser-based scheme. PartsSupplier.com is a regular supplier of parts to Workplace.com. In this case, a role-based access- control (RBAC) scheme is used for access to information. An engineer of Workplace.com authenticates at the employee portal at Workplace.com and clicks on a link to access information at PartsSupplier.com. Because the user is authenticated in the role of an engineer, he is taken to the technical documentation and trou- bleshooting portion of PartsSupplier.com’s Web site without having to sign on.
Similarly, an employee in a purchasing role signs on at Workplace.com and is authorized, in that role, to place purchases at PartsSupplier.com without having to authenticate to PartsSupplier.com. For this scenario, PartsSupplier.com does not have identity information for individual employees at Workplace.com. Rather, the linkage between the two federated partners is in terms of roles.
The scenario illustrated in Figure 15.5c can be referred to as document based rather than browser based. In this third example, Workplace.com has a purchasing agreement with PinSupplies.com, and PinSupplies.com has a business relationship with E-Ship.com. An employee of WorkPlace.com signs on and is authenticated to make purchases. The employee goes to a procurement application that provides a list of WorkPlace.com’s suppliers and the parts that can be ordered. The user clicks on the PinSupplies button and is presented with a purchase order Web page (HTML page). The employee fills out the form and clicks the submit button.The procurement application generates an XML/SOAP document that it inserts into the envelope body of an XML-based message. The procurement application then inserts the user’s credentials in the envelope header of the message, together with Workplace.com’s organizational identity. The procurement application posts the message to the PinSupplies.com’s purchasing Web service. This service authenticates the incoming message and processes the request. The purchasing Web service then sends a SOAP message to its shipping partner to fulfill the order. The message includes a PinSupplies.com security token in the envelope header and the list of items to be shipped as well as the end user’s shipping information in the envelope body. The ship- ping Web service authenticates the request and processes the shipment order.