Adding Azure Subscription as a Parameter of Task Group in VSTS

You can use variable in Azure Subscription, but the value should be the actual value of related endpoint.

1. Create a new release/build definition with debug enabled (set/add system.debug variable to true) and add Azure PowerShell task to get the actual value.
2. Start/Queue release/build, then check the log, you can find the log like this: ##[debug]INPUT_CONNECTEDSERVICENAMEARM: '{actual value}’
3. Edit task group, specify variable in Azure Subscription input box (e.g. $(sub)) >Save
4. Edit your release definition, add the variable(s) (e.g. mySub) with that actual value (step 1)
5. Tasks > Select related Task group > Specify variable (e.g. $(mySub)) in sub (per to step 3) input box.

On the other hand, you can choose azure subscription for related task group directly (step 3, then edit tasks for an environment > Choose Azure Subscription directly)

While there are examples out there that suggest you can use a variable for the service connection name, there is also some documentation out there that suggests that variables for service connections are not supported (https://docs.microsoft.com/en-us/azure/devops/pipelines/library/service-endpoints?view=azure-devops&tabs=yaml#use-a-service-connection, for example).

I've run up against this in my own pipelines and solved it using template expressions:

    ${{ if eq(parameters.environmentType, 'dev') }}:      azureResourceManagerConnection: Azure Dev    ${{ if eq(parameters.environmentType, 'test') }}:      azureResourceManagerConnection: Azure Test    ${{ if eq(parameters.environmentType, 'prod') }}:      azureResourceManagerConnection: Azure Prod