Use CertStore to retrieve certificate instead of reading from FileSystem

[fume]

Reading from Cert Store is a better option even when SPIDProxy is deployed in Azure. Cert is stored in KeyVault, then imported into App Service (see Import a certificate from your vault to your app). The good thing is that you update the Cert in KeyVault, and then it's automatically imported into App Service.

You need just to declare in Configuration the Tumbprint of certificates to be made available to code. Then, you use the approach described here (Use a TLS/SSL certificate in your code in App Service): this approach doesn't make any assumption code is running in Azure, so it satisfies the requirement.