As we know, Azure Web Apps or Azure App Service comes with a unique subdomain, azurewebsites.net and it gives a wildcard certificate too. However, we can purchase and manage an SSL certificate from the Microsoft Azure portal itself for custom domains. Go to Azure web application in the Azure portal, go to SETTINGS, and click on SSL certificates:
For more details on buying and configuring an SSL certificate for your Azure App Service refer to https://docs.microsoft.com/en-us/azure/app-service-web/web-sites-purchase-ssl-web-site.
