C# Using Single SignOn (SSPI) for Virtual Center 2.5.0.119598

I am trying to use passthru authentication using SSPI to work in my c# application. Here is a snippet of the code I am trying to get to work.

returns a reference for VMware.Vim.SessionManager

VMware.Vim.VimClient vimClient = new VMware.Vim.VimClient();

vimClient.Connect("10.x.x.x", CommunicationProtocol.Https, 443);

ManagedObjectReference serviceInstance = new ManagedObjectReference();

serviceInstance.Type = "ServiceInstance";

serviceInstance.Value = "ServiceInstance";

SessionManager sm = new SessionManager(vimClient, serviceInstance);

sm.LoginBySSPI(ct_b64, null);

I get an exception when I try to call this method LoginBySSPI

I am not sure that this is the correct approach, but I really would like to be able to login using single signon in my c# code but not having much success.

This works fine using PowerShell but I want to be able to do this directly using c# without using PS Pipelines.

Any suggesstions welcome.

Thanks