Consolidation of multiple providers is the primary advantage of using a third-party identity service. A third-party identity service is a service that provides identity and access management (IAM) functions, such as authentication, authorization, and federation, for multiple applications or systems, using a single identity provider (IdP). A third-party identity service can offer various benefits, such as:

Improving the user experience and convenience by allowing the users to access multiple applications or systems with a single sign-on (SSO) or a federated identity

Enhancing the security and compliance by applying the consistent and standardized IAM policies and controls across multiple applications or systems

Increasing the scalability and flexibility by enabling the integration and interoperability of multiple applications or systems with different platforms and technologies

Reducing the cost and complexity by outsourcing the IAM functions to a third-party provider, and avoiding the duplication and maintenance of multiple IAM systems

Consolidation of multiple providers is the primary advantage of using a third-party identity service, because it can simplify and streamline the IAM architecture and processes, by reducing the number of IdPs and IAM systems that are involved in managing the identities and access for multiple applications or systems. Consolidation of multiple providers can also help to avoid the issues or risks that might arise from having multiple IdPs and IAM systems, such as the inconsistency, redundancy, or conflict of the IAM policies and controls, or the inefficiency, vulnerability, or disruption of the IAM functions.

The other options are not the primary advantages of using a third-party identity service, but rather secondary or specific advantages for different aspects or scenarios of using a third-party identity service. Directory synchronization is an advantage of using a third-party identity service, but it is more relevant for the scenario where the organization has an existing directory service, such as LDAP or Active Directory, that stores and manages the user accounts and attributes, and wants to synchronize them with the third-party identity service, to enable the SSO or federation for the users. Web based logon is an advantage of using a third-party identity service, but it is more relevant for the aspect where the third-party identity service uses a web-based protocol, such as SAML or OAuth, to facilitate the SSO or federation for the users, by redirecting them to a web-based logon page, where they can enter their credentials or consent. Automated account management is an advantage of using a third-party identity service, but it is more relevant for the aspect where the third-party identity service provides the IAM functions, such as provisioning, deprovisioning, or updating, for the user accounts and access rights, using an automated or self-service mechanism, such as SCIM or JIT.