SSO Service

Description

The SSO Service (SSOS) is the operational instantiation of the Single Sign-On (SSO) concept within a 3GPP system. It encompasses the complete set of network functions, protocols, and interfaces required to deliver SSO as a usable service to subscribers and third-party service providers. While SSO defines the architectural principles, SSOS refers to the deployable service that executes those principles. It acts as the intermediary that brokers trust between the user's identity provider (typically the home network) and the various service providers (SPs) the user wishes to access.

Technically, the SSOS is implemented through dedicated functional elements, often collocated with or integrated into existing network nodes. A core component is the SSO Service Function, which includes the logic for session management, token generation (using standards like SAML or OpenID Connect), and policy enforcement. It interfaces with the authentication infrastructure, such as the Home Subscriber Server (HSS) or Unified Data Management (UDM), to verify user credentials. It also exposes standardized interfaces (e.g., based on Diameter or HTTP/2) for service providers to request authentication and validate tokens.

The service works by intercepting access requests to protected services. When an unauthenticated request arrives, the SSOS redirects the user agent to an authentication portal. After successful authentication (e.g., via SIM, password, or biometrics), the SSOS creates a secure session and issues a cryptographic token. This token is then used to seamlessly access other services without re-authentication, as the SSOS validates the token for each subsequent request. The service manages the entire lifecycle, including token expiration, renewal, and revocation.

Key to the SSOS is its role in service federation. It maintains a trust relationship with external SPs, often established through pre-shared certificates or dynamic discovery protocols. The SSOS also handles user consent, logging, and auditing to meet regulatory requirements. In a 5G context, the SSOS may be implemented as a network function within the Service-Based Architecture (SBA), interacting with the Network Repository Function (NRF) for discovery and the Security Edge Protection Proxy (SEPP) for inter-network security.

Purpose & Motivation

The SSO Service was created to provide a standardized, operable service layer for Single Sign-On, moving beyond theoretical frameworks to practical deployment. While SSO specifications defined the 'what,' SSOS addresses the 'how' by detailing the service characteristics, operational procedures, and management aspects. It solves the problem of inconsistent and proprietary SSO implementations that hindered interoperability between different network operators and service providers.

Prior to its specification, operators developing SSO capabilities faced ambiguity in implementation details, leading to fragmented user experiences and increased integration costs for application developers. The SSOS provides a clear blueprint for building a compliant SSO service, ensuring that all necessary components—like token formats, error handling, and charging interfaces—are consistently implemented. This enables a marketplace of interoperable services where users can leverage their mobile identity across a wide ecosystem.

Motivated by the commercial need to monetize network authentication assets, SSOS allows operators to offer SSO as a value-added service to enterprises and content providers. It facilitates new business models, such as identity-as-a-service. By standardizing the service, 3GPP ensured that security and privacy controls are uniformly applied, protecting user data across federated environments. It essentially turns the SSO security framework into a billable, manageable network service.