why user creation activity in the SQL Server security layer is necessary. Without this step, Application A’s API cannot communicate with the database.

Question

I am reaching out to seek formal response on an issue related to integration and database connectivity. Below is the background for context: 

 

Application A is built using ASP.NET Core (.NET Framework 8) and communicates with multiple source applications by fetching data through APIs. 

1. Application A operates with its own application pool, allowing it to connect to other application pools, such as APPLICATION B and APPLICATION C, via the application pool user ISS APPPOOL/*****APPLICATION A’s*** **API. 
2. Since Application A is an integrated application, its application pool user is used to fetch data from multiple source databases, including APPLICATION B and APPLICATION C. 

This requires database mapping, where a database user must be created at the database level. 

Please refer to the links below for details on the deployment of Application A so far: https://learn.microsoft.com/en-us/iis/manage/configuring-security/application-pool-identities

 

We would like to understand why user creation activity in the SQL Server security layer is necessary. Without this step, Application A’s API cannot communicate with the database. Is this dependency related to changes introduced after .NET Core version 0.5? For reference, please check the following link: 

(htt[ps://learn.microsoft.com/en-us/iis/manage/configuring-security/application-pool-identities]](https://learn.microsoft.com/en-us/iis/manage/configuring-security/application-pool-identities"learn.microsoft.com")

 

I request Microsoft Community to provide assistance/resolution for this issue , which is becoming a show stopper ?