Add a "CertificateUrl" optional manifest value for MSIX/AppX apps, for when app devs store the certs separately from the apps.

Relevant area(s)

WinGet CLI

Description of the new feature / enhancement

Though it's relatively common that .appx/.msix files released by various devs lack signatures or have signature errors (which make them uninstallable through Winget, and possibly at all), I've come across a handful of cases where the devs do have signatures, but inexplicably forgot to include them in the app files for reasons that are unknown to me.

Adding a "CertificateUrl" optional value to the "Installer" YAML would presumably make it possible to install those apps in Winget.

Instances of affected apps:

• PeaZip's MSIX version:
• • https://github.com/giorgiotani/PeaZip/releases/download/10.9.0/PeaZip_10.9.0.0_x64__m1xx1d1szsx2y.msix
• • https://sourceforge.net/projects/peazip/files/Resources/MSIX%20app%20certificate/peazip.cer/download
• • (Documentation of its officiality) https://peazip.github.io/peazip-64bit.html (near the bottom of that page)
• VLC's UWP app:
• • https://get.videolan.org/vlc-winrt/3.1.0/VLC.Universal_3.1.0.0_x64_Test/VLC.Universal_3.1.0.0_x64.appx
• • https://get.videolan.org/vlc-winrt/3.1.0/VLC.Universal_3.1.0.0_x64_Test/VLC.Universal_3.1.0.0_x64.cer
• LibreWolf's MSIX version:
• • https://dl.librewolf.net/librewolf/148.0-1/librewolf-148.0-1-windows-x86_64-msix.msix
• • https://dl.librewolf.net/librewolf/148.0-1/librewolf-148.0-1-windows-x86_64-msix.msix.sig

Proposed technical implementation details

In the Installer template YAML for Manifest 1.12 or 1.13, add a CertificateUrl: or CertUrl:, optional value.

Logically, validations would need to check for if it's indeed a valid .cer and/or .sig filetype file, and that the value only applies for .msix/.msixbundle/.appx/.appxbundle installer types.

Start with the Installer template YAML for Manifest 1.12 or 1.13, then trace validation and installation handling for .msix, .msixbundle, .appx, and .appxbundle installers. Determine how an optional CertificateUrl value should be validated and consumed, including whether .cer and .sig files are supported; the work is done when manifests can use the external certificate safely and other installer types reject it.