How do I add a new Windows user?

We have a service account that does our TFS builds, part of which is using Octo.exe to publish a release to Octopus through the API. However, we have to use an API key that is for one of the users Configuration/Users. How do I add the service account as a Windows user so that it can have its own API key?

I just added the user with username and password, but since it is a Windows user, I wouldn’t expect to have to add the password.

I will try a build with this and see what happens.