I am developing a Windows Phone 8.1 app using Xamarin Forms inside of Visual Studio 2015. I cannot seem to sign the app. I do not have a "Choose Certificate" button on the Package tab of the appxmanifest file like all of the articles I have read say I should.
I ultimately just need to upload the appx package to my company's Azure Intune. I can generate the appx package and I can upload it but it fails with the error "no signature in the subject". From my research, I believe this means it is not signed. However, other articles indicate that by right-clicking on the project > Store > Create App Package > Yes (to deploy to store as I do have a developer account) that this should automatically sign the package. The error I get in the Windows event viewer is that the Publisher in the appxmanifest does not match the publisher of the signing certificate. I can see what each publisher values are, I just can't seem to change them.
If you just need to upload your package to your company's Azure Intune, you could create a certificate by yourself to sign your appx package.
See create a self signed certificate and Sign an app package using SignTool.
To publish your app to the Windows Store, you need to associate your app with an existing app name in Dev Center (or you can reserve a new one). The association will automatically align all the app identity info. The Windows Phone 8.1 project does not have the "Choose Certificate" button and it even doesn't include the test certificate in the project. But after association, you could create your appx package and upload it in Dashboard as usual.
You might refer to my response in this post as well.