Call On Prem Web Application(ASP.Net Web APIs) from Azure environment(.Net Core Web APIs, Azure Function Apps)

Question

Hi All,

We are creating REST endpoint with help of ASP.Net core Web API, while working on some feature we have to consume endpoint(APIs) which already hosted and running on prem windows server, so we plan to reuse with all security concerns.

1. New certificate created and installed on on-prem, SSL certificate integrated in on-prem hosted APIs,
2. Upload the certificate into azure key-vault
3. Read the certificate from Azure key-vault
4. Use certificate in Http-Client request header to consume on-prem APIs

"We got SSL connection could not be established "

Any suggestions on implement.