I looked all over the web for concrete information regarding CALs licenses in Azure SQL but couldn't find much event on Microsoft Azure site. Is this included within subscription ? Or Is it part of Azure Active Directory ?
There are no license restrictions in Azure SQL Database. No CAL licenses are required. You pay for the database, and you may use it for any kind of application you wish and for any number of hosts or users. You only need to take in consideration Azure SQL Database limits for the maximum number of concurrent sessions allowed on each tier. Here are the limits for the DTU model and here you will find limits for the vCore model.