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X/Open Single Sign-on Service (XSSO) -<br> Pluggable Authentication Modules

X/Open Single Sign-on Service (XSSO) -
Pluggable Authentication Modules
Copyright © 1997 The Open Group

XSSO Account Management Services

The essential objective of XSSO Account Management services is to provide support for the development of applications to implement co-ordinated management of account information bases in a heterogeneous set of security domains (platforms and applications).

As described in Introduction to Single Sign-on , an individual end-user of a distributed system typically requires the capability to utilize many different platforms and applications (domains). To provide this capability an individual needs to be represented by entries in the account information bases appropriate to each of those domains.

Each individual domain will have its own set of account attributes to be managed. These are referenced to domain specific identities and have domain specific formats. The requirement on XSSO is to provide the capability of managing a minimum common core set of such attributes with the capability for future extension.

The business benefit sought from the specification of the XSSO ACM Service is a reduction in the number of administrative interactions with the system to manage individual accounts. In an approach based on a minimum common core set of attributes, the extent to which these benefits are realisable within a particular system depend upon an assumption that any additional attributes required for accounts by a particular domain can be generated on basis of domain defined defaults or derived from XSSO provided attribute values on the basis of domain defined rules. As an example, under DCE the creation of a login account requires the previous creation of the appropriate principal, group and organization registry entries.

Scope of XSSO Account Management

XBSS Functional Requirements

The core requirements of XSSO Account Management are based upon requirements detailed in the XBSS. These encompass both Account Level Policies and System Level Policies.
Account-level Policy
The following requirements are applicable to the administration of individual accounts:
System-level Policy
The following XBSS requirements are applicable and controlled on a policy domain wide basis:

Basic Functional Requirements

The XSSO ACM-API is required to support the following functions within the domain supporting the interface:

Add Account

Create a new account.

Delete Account

Delete account.
If done thoroughly, this encompasses the deletion or reassignment of system resources currently assigned to the account according to the applicable policy. For example, files owned by the account should be deleted or have their ownership changed. Access authorizations specifically assigned for the account should be removed. For example, this may imply a change of ACLs and file ownership attributes.

Update Account

Change the value of account attributes.

List Accounts

List all accounts or accounts based on optional selection criteria. This may include the selective listing of "active accounts" for those domains in which the interpretation of an "active account" is defined.

Disable/Enable Account

Disable and enable the use of an account to access the services of the domain. The disabling of an account should include, where possible, the disabling of any scheduled sessions for the account and the termination of any interactive sessions for the account that are in progress at the time the account is disabled.

Update Account Authentication Information

This includes update of account authentication information by an administrator, including a forced change on first usage, and by the end-user via XSSO Sign-on Services. An administrator may also be able to update the method or methods of authentication. In the first version of XSSO the only form of authentication information required to be supported are passwords and pass phrases but the specification should not preclude future extensibility.

Add Account Attribute

Create a new attribute that may be assigned to accounts.

Delete Account Attribute

Delete an attribute. Where possible this should include the removal of this attribute from all accounts, or should only succeed if the attribute is not currently assigned to any account.

Set Account Attributes

Set the values of attributes for an account.

Get Account Attributes

Retrieve the attributes assigned to an account.

Account Management Authorities

The account management authorities identified below are disjoint authorities that are used to control the exercise of Account Management Functions in support of the principles of Least privilege and Separation of Duties.

Required to create, populate, and modify accounts. Excludes modification of audit attributes, authentication information and account enabling, disabling and deletion.

Required to assign attributes to accounts. This authority may be parameterized to control the modification of discrete sets of attributes.
The next two authorities can be considered as specific examples of the XSSO_ATTRIBUTE_ADMIN authority with the sets of attributes which they cover having particular security significance.

Required to modify account audit attributes.

Required to set and modify account authentication information attributes, and to enable, disable, and delete accounts.

Required to configure XSSO UAM services. For example to add/modify/delete domain types and domain instances.

Common Core Account Attributes

The common core attributes for accounts represent the minimum set of attributes required by XBSS for the purposes of both account level and system level policy enforcement. These attributes are not necessarily applicable nor mappable to all component account registries within a policy domain but a XSSO implementation has to be capable of supporting their management. The common core attributes comprise:


Human readable text string. Must be unique within the domain of definition.


Domain internal accountID that must be unique within the domain of definition.

Account Enabled Flag

Account enabled if flag set, account disabled if unset.

Account Last Used

Date and time the account was last used in an authentication operation.

Authentication Information

For the current specification this comprises at least a password. In the future it may include information such as authentication method.

Authentication Information Expiry

The date and time at which the current authentication information expires at which system level policy may enforce an authentication information change. Appropriate setting of this attribute can force an authentication information change on the next use of the account for a authentication operation.

Account Audit Identity

Identity assigned to an account for audit purposes within domain. (May be the same as Account_ID.)

Account Audit Pre-selection Mask

Configuration of audit profile for account for those component services that support the control of audit service by account.

Authorization Attributes

Set of authorizations assigned to account. These may include access identities, roles identities, service specific privileges, and so on. These may be specific to each component service within a XSSO policy domain.

Account Environment Data

Information that defines the environment to be created on session establishment within which the account is required to operate. For example, shell or application, home directory, environment variables, resource quotas, default resource access permissions, and so on. These will be specific to each component service within a XSSO policy domain.

The interface style required to support XSSO is that in which the minimum information necessary to identify the account is always required and all parameters, whether core or extended are passed as a list of attribute/value pairs as and when required.

The issue of atomicity of operations and locking has been discussed and the need to identify any implicit locking mechanisms in the use of the interface identified. This is only of concern in update operations. The semantics of the operation require defining. There are two possible approaches:

Management of Account Information for Multiple Services

A concept of XSSO Account Administration is that XSSO provides a common management interface to account information for all the component services within an XSSO Policy Domain.

Each component service may identify its account attributes by different labels and represent them in different formats. Each domain may also utilize different naming schemes for account identities. It is therefore necessary that functionality is included in an implementation of XSSO UAM to enable an administrator to configure the mapping and XSSO sign-on components, such as PAM, to be able to get the mapping to support secondary sign-on operations.

Such mappings may be based on two approaches:


In which the secondary domain representation of an identity or attribute may be derived from the primary domain representation on the basis of a transformation rule


In which the mapping cannot be derived on the basis of a transformation rule but has to be explicitly defined.

The XSSO administrative application management information base requires to hold the following information:

Register of Domain Types

This is a register of the different types of domains that are integrated with and managed by the XSSO administrative application. For each domain type, a list of the domain attributes is maintained.

Register of Domain Instances

This is a register of instances of domains managed by the XSSO administrative application. For each instance of a domain, its location and domain type is maintained.

Register of Accounts

This is a register of the accounts managed by the XSSO administrative application. For each account a list of the domain instances within which it is registered and the attributes assigned to it within each domain instance are maintained. This may include copies of the credentials required to authenticate to the domain if required to support secondary sign-on.

The XSSO may not necessarily maintain a copy of the attributes assigned within each domain instance provided that it can retrieve the information from the domain itself when required.

Default Account Profiles

To facilitate the assignment of attributes across multiple domains to accounts and the simultaneous registration of principals in multiple domains then a set of account profiles may be defined. These may include rules for derivation or look up of secondary domain specific attributes based on XSSO domain based attributes.

Registry of Domain Types

For each domain typ, a set of attributes is required to be registered. For each attribute the following information may be required:


The domain type to which the attribute belongs.


The internal label by which the attribute is referenced.


The human readable label used to reference the attribute.

Attribute_Format (Encoding)

The format in which the attribute value is represented for storage and exchange.


The rule by which the default value of this attribute is derived.


The domain specific authorities that have to be possessed by a caller of the ACM-API in order to query or modify this attribute.

XSSO Account Management Implementation Considerations

Mapping of Administrative Authorities to XSSO UAM Agents

An XSSO implementation needs to be able to map the domain specific authorities required to manage the attributes within the domain to the XSSO administrative authorities and roles that it supports. That is, an XSSO agent requires sufficient privilege to manage the domain that it services. The exercise of those privileges must be matched to the authorization assigned to the initiating administrator principals.

The security context of an XSSO agent invoked within a specific domain on behalf of an XSSO Administrator is required to reflect the security context of the XSSO Administrator.

XSSO Management Information Base Initialization

An implementation is required to define how the XSSO Management Information Base is initialized.
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