This script can be used to create an Azure web app and add the .NET core 3.0 extensions in an Azure DevOps release pipeline. See https://chamindac.blogspot.com/2019/08/creating-azure-web-app-supporting-net.html

CreateAzureWebAppForNetCore3.ps1

param (
    [Parameter(Mandatory=$true)]
    [string] $azureAppId,
    [Parameter(Mandatory=$true)]
    [string] $azureAppPwd,
    [Parameter(Mandatory=$true)]
    [string] $azureTenant,
    [Parameter(Mandatory=$true)]
    [string] $resourceGroupName,
    [Parameter(Mandatory=$true)]
    [string] $location,
    [Parameter(Mandatory=$true)]
    [string] $webAppPlanName,
    [Parameter(Mandatory=$true)]
    [string] $webAppPlanSKU,
    [Parameter(Mandatory=$true)]
    [string] $webAppName,
    [Parameter(Mandatory=$true)]
    [string] $core3Extension,
    [string[]] $webAppDeploymentSlotNames = @(),
    [string] $azureRestApiVersion = '2018-11-01'
)


Try {
 
    az login --service-principal -u $azureAppId --password $azureAppPwd --tenant $azureTenant

    if ($LastExitCode -ne 0) {
            throw $Error[1]
        }

    # Create if resource group not found
    if ((az group exists -n $resourceGroupName) -ne 'true') 
    { 
        Write-Host ("Resource group " + $resourceGroupName + " not found. Creating it...")

        az group create -n $resourceGroupName -l $location

        if ($LastExitCode -ne 0) {
            throw $Error[1]
        }

        Write-Host ("Resource group " + $resourceGroupName + " created.")
    }
    else
    {
        Write-Host ("Resource group " + $resourceGroupName + " is found.")
    }


    # Create Web App Plan if not exisit
    $webAppPlans = az appservice plan list -g $resourceGroupName | ConvertFrom-Json

    if (($webAppPlans.Count -gt 0) -and ($webAppPlans.name.Contains($webAppPlanName)))
    {
        # update app service plan pricing
        Write-Host ("Web App Plan " + $webAppPlanName + " is found. Updating pricing..." )
        
        az appservice plan update -n $webAppPlanName -g $resourceGroupName --sku $webAppPlanSKU
        
        if ($LastExitCode -ne 0) {
            throw $Error[1]
        }
        Write-Host ("Done.")
    }
    else
    {
        Write-Host ("Web App Plan " + $webAppPlanName + " not found. Creating it...")

        az appservice plan create -n $webAppPlanName -g $resourceGroupName --sku $webAppPlanSKU
        
        if ($LastExitCode -ne 0) {
            throw $Error[1]
        }
        Write-Host ("Web App Plan " + $webAppPlanName + " created.")
    }

    # create if web app does not exist
    $webApps = az webapp list -g $resourceGroupName | ConvertFrom-Json
    
    if (($webApps.Count -gt 0) -and ($webApps.name.Contains($webAppName)))
    {
        Write-Host ("Web App " + $webAppName + " is found." )
    }
    else
    {
        $webAppPricePlan = az appservice plan show -n $webAppPlanName -g $resourceGroupName | ConvertFrom-Json
        
        Write-Host ("Web App " + $webAppName + " is not found. Creating it...")

        az webapp create -n $webAppName -g $resourceGroupName -p ($webAppPricePlan.id) 
                

        if ($LastExitCode -ne 0) {
            throw $Error[1]
        }
        Write-Host ("Web App " + $webAppName + " is created.")
    }

    # Check if Site Extension added for ASP.NET Core and install it if not

    $siteExtensions = Get-AzureRmResource -ResourceType "Microsoft.Web/sites/siteextensions" `
    -ResourceGroupName $resourceGroupName -Name $webAppName -ApiVersion $azureRestApiVersion

    if (($siteExtensions -eq $null) -or (-not $siteExtensions.Properties.id.Contains($core3Extension)))
    {
        Write-Host ("Site extension " + $core3Extension + " is not added to web app " + $webAppName + ". Adding...")
        $siteExtensions = New-AzureRmResource -ResourceType "Microsoft.Web/sites/siteextensions" `
        -ResourceGroupName $resourceGroupName -Name ("$webAppName/$core3Extension") -ApiVersion $azureRestApiVersion -Force
        
        if ($LastExitCode -ne 0) {
                throw $Error[1]
            }
        Write-Host ("Done.")
    }
    else
    {
        Write-Host ("Site extension " + $core3Extension + " is already added to web app " + $webAppName + ".")
    }

    foreach ($webAppDeploymentSlotName in $webAppDeploymentSlotNames)
    {
        if (-not ([string]::IsNullOrWhiteSpace($webAppDeploymentSlotName)))
        {
            # Check if any depyment slots exists
            $slots = az webapp deployment slot list -g $resourceGroupName -n $webAppName | ConvertFrom-Json

            if (($slots.Count -gt 0) -and ($slots.name.Contains($webAppDeploymentSlotName)))
            {
                Write-Host ("Web App " + $webAppName + " slot " + $webAppDeploymentSlotName + " is found." )
            }
            else
            {
                Write-Host ("Web App " + $webAppName + " slot " + $webAppDeploymentSlotName + " is not found. Creating it...")

                az webapp deployment slot create -s $webAppDeploymentSlotName -n $webAppName -g $resourceGroupName `
                --configuration-source $webAppName
                

                if ($LastExitCode -ne 0) {
                    throw $Error[1]
                }
                Write-Host ("Web App " + $webAppName + " slot " + $webAppDeploymentSlotName + " is created.")
            }

            # Check if slot Extension added for ASP.NET Core and install it if not

            $slotExtensions = Get-AzureRmResource -ResourceType "Microsoft.Web/sites/slots/siteextensions" `
            -ResourceGroupName $resourceGroupName -Name ("$webAppName/$webAppDeploymentSlotName") `
            -ApiVersion $azureRestApiVersion

            if (($slotExtensions -eq $null) -or (-not $slotExtensions.Properties.id.Contains($core3Extension)))
            {
                Write-Host ("Slot extension " + $core3Extension + " is not added to web app slot " + ("$webAppName/$webAppDeploymentSlotName") + ". Adding...")
                $slotExtensions = New-AzureRmResource -ResourceType "Microsoft.Web/sites/slots/siteextensions" `
                -ResourceGroupName $resourceGroupName -Name ("$webAppName/$webAppDeploymentSlotName/$core3Extension") `
                -ApiVersion $azureRestApiVersion -Force
        
                if ($LastExitCode -ne 0) {
                        throw $Error[1]
                    }
                Write-Host ("Done.")
            }
            else
            {
                Write-Host ("Site extension " + $core3Extension + " is already added to web app slot " + ("$webAppName/$webAppDeploymentSlotName") + ".")
            }
        }
    }
    
}
catch
{
    Write-Host $Error[0] -ForegroundColor Red
    exit 1
}