@Anonymous , Based on my understanding of your question.
In the multi-tenant App service, you can’t modify the trusted root store due to sandbox restrictions. However, on ASE can you modify the trusted root store.
App Service has a list of Trusted Root Certificates
which you cannot modify
in the multi-tenant
variant version of App Service, but you can load your own CA certificate in the Trusted Root Store in an App Service Environment (ASE), So, what you’re trying to accomplish won’t be possible without an ASE or cert signed by a trusted CA.
Kindly check this document for more details.
Azure Web App sandbox and Operating system functionality on Azure App Service