Provide API security

[tomkerkhove]

The API should be secured with a shared access key

[pvandenheede]

@tomkerkhove My proposal would be to use Azure key vault to store the API key (shared secret).
To be used in the HTTP header. Header name would be free to choose in web.config.

Unless you want me to put everything (name+value) in web.config? That way we don't create any dependencies to other Azure resources?
Up to you.