I want to build and deploy an iOS app only for my company specific users.
I do not want to publish it for normal users on the iOS App Store. How can I do this?
You are looking for Apple Developer Enterprise Program.
This program, created specifically with the said need in mind lets you distribute and manage apps internally in your organization, without going through public faing iOS App Store.
If you are looking for a quick and easy solution and are familiar with generating .ipa files (ad-hoc deployment), you can use Diawi for deploying it on the specific devices. Please keep in mind that the device-UDIDs need to be registered in your apple developer account. https://www.diawi.com/ (apps can be password protected aswell)