Update Dec 28th 2020: Visual Studio 2019 no longer generates certificates by default when creating a UWP project (yay), so you don’t end up broken out of the box! Plus, when you go through the ‘Create App Package’ flow, it will ask to create certifcates – when prompted for a password, just don’t enter one, and it’ll do the right thing. Hurrah!

Have you ever created a UWP project that you check into a Source Control system? Tried to build it on multiple devices, or share with a team? I’m pretty sure you’ve seen the warning from Visual Studio during build saying “Couldn’t find Foo_TemporaryKey.pfx” (*.pfx is in the default .gitignore), or “Cannot import the key file “Foo_TemporaryKey.pfx"”.

I find this frustrating because it makes it difficult to get the quick check of “No warnings, or messages, I must be good” by looking at your output window.

Thanks to some stuff I had to figure out at work, I found the right way to generate the keys/certs that you can check in, and don’t require a password. This also has the advantage of working well in a build server environment.

I know, I know “But it’s a cert! It’s super special!”. Sure, but these are your self-signed certs. These are used for, at worse, side loading on PC you own. They’re also unchained — there’s no real root cert, so you have to install them, which requires admin rights. There’s minimal spoofing risk, since I dearly hope you’re not using this for broad distribution.

Before you ask, these certs are only for signing the package, and when you publish through the store, the package is signed with a real cert from Microsoft, not this certificate.

Anyway, this is a tl;dr based on an MSDN article, which while it claims it is out of date (it probably is), it works:

1. Open up a developer Command Prompt
2. Change to the directory where you want the files
3. Run makecert -sv <a name>.pvk -n “CN=SomeName” <a name>.cer -a sha256 /r /h 0 /eku “1.3.6.1.5.5.7.3.3,1.3.6.1.4.1.311.10.3.13”
4. When prompted, don’t enter a password — select ‘None’ (This is the key step to making this smooth
5. Then, in that same directory, run pvk2pfx -pvk <a name>.pvk -spc <a name>.cer -pfx <a name>.pfx
6. In VS, open the package.appxmanifest, and change to the packaging tab
7. Click ‘Choose Certificate…’
8. Select your file
9. BOOM!

Note: If you’re working in a git repository created by VS, it’s default .gitignore file excludes this file from being added to to the repo. You’ll need to use git on the command line to get it added/staged (ditto, for future updates):

git add <a name.pfx> --force