What additional information is needed to join an existing vCenter Single Sign-On domain?

To successfully join an existing vCenter Single Sign-On (SSO) domain, it's essential to establish a secure connection between the vCenter Server and the SSO. The most critical component in this scenario is the HTTPS port, which is typically port 443. This port is used for secure communications over the web, utilizing the HTTPS protocol.

When joining a vCenter SSO domain, the use of HTTPS ensures that all data exchanged between the vCenter and the SSO server is encrypted, providing a secure channel for authentication and domain management processes. It also allows for necessary interactions required for the SSO service, such as querying for existing users and groups or validating credentials.

In contrast, while the other options involve ports that are critical for other functionalities within a network or directory service, they are not specifically tied to the action of joining an SSO domain in the context of vCenter. The LDAP port, for instance, is important for directory services but does not directly apply to the connection utilized during the joining process. Thus, the use of the HTTPS port is the essential requirement for this particular operation.