Hi @azure ,
I believe https://learn.microsoft.com/en-us/azure/app-service/configure-ssl-certificate#store-in-azure-key-vault would be a good place to start for becoming familiar with using cert from key vault in your app service. There are plenty of key vault code samples that you can find here.
By basic authentication, you could create username/password combo pair and store it key vault, retrieve those values, and if they don't match, return a 404. Have a look at the following samples to see how to achieve what you're trying to do.
- https://learn.microsoft.com/en-us/samples/azure-samples/azure-sdk-for-js-keyvault-secret-get-set-managedid/get-set-keyvault-secrets-managed-id-nodejs/
- https://learn.microsoft.com/en-us/samples/azure/azure-sdk-for-js/keyvault-certificates-javascript/
- https://learn.microsoft.com/en-us/samples/azure/azure-sdk-for-js/keyvault-secrets-javascript/