There is another way to log in without manually input credentials in a web form and the command for that is as follows:
appbuilder dev-telerik-login <user> <pass>
I do believe you can automate the process as you have all needed commands available, but I am not aware of powerShell and won't be able to provide a complete solution.
There are a lot of resources on the matter like this one
and I am sure you will be able to find a solution on the web.
Please let me know if I can be of further assistance.