ESXi handles user authentication and supports user permissions.
When you connect directly to an ESXi host with the vSphere Client, you can create users and groups that are local to that ESXi host. You can also assign permissions to these users and groups.
vCenter Server is not aware of users that are local to ESXi, and ESXi is not aware of vCenter Server users. For more information on managing users for ESXi hosts managed by vCenter Server, see the vSphere Security documentation.