What is a Service Connection in Azure used for?

Question

I see that Service Connection is a link between Azure Pipelines and Azure Subscription to trigger Pipelines. But can I create a Service Connection and get client id and secret and use that to obtain access token. And with that access token I can run the Azure Pipeline via c# code with REST APIs? Is this what a service connection used for ?

Answer 1

But can I create a Service Connection and get client id and secret and use that to obtain access token.

You can generate token via this, but you can't use it in C# code to run the pipeline.

Service connection between 'Azure Pipelines and Azure Subscription' just for you to create an app in AAD, this will also create related Enterprise App(service principal) in Azure portal side.

The service principal can be assigned permissions in the Azure portal to access resources. Once the service principal has access to a resource at the Azure Portal, the devops pipeline using the service connection associated with the service principal will also have the same access.

The original purpose of the above is service connection design is to allow the pipeline to have access to the resources at the portal.

Why we can't use the app's clientid and secret to get an access token to run the pipeline?

It is clearly in this official document:

https://learn.microsoft.com/en-us/azure/devops/integrate/get-started/authentication/authentication-guidance?view=azure-devops

The Azure DevOps API doesn't support non-interactive service access via service principals.