Launching boxstarter with bad param isn't instantly evident

[crutkas]

What You Are Seeing?

While working on https://github.com/Microsoft/windows-dev-box-setup-scripts, i misconfigured a test URL and couldn't figure out why it looked like work was being done but would look to fail without processing anything.

What is Expected?

Immediately inform the file passed in doesn't exist rather than prompting for user password or turning off Windows Update.

How Did You Get This To Happen? (Steps to Reproduce)

do something like this:
http://boxstarter.org/package/url?https://raw.githubusercontent.com/Microsoft/windows-dev-box-setup-scripts/master/dev_app
when http://boxstarter.org/package/url?https://raw.githubusercontent.com/Microsoft/windows-dev-box-setup-scripts/master/dev_app.ps1 is the actual correct URL.

[mwallner]

Currently the "validity" of an URL / file is checked in New-PackageFromScript, which is called way in the Boxstarter workflow.

We'll have to do this at the very beginning, before password prompt, CredSSP check etc.
Probably it's best to generate all required temp packages before doing anything else.