SharePoint 2013 licensing model has changed bit for user scenarios. it has been slightly change from the SharePoint 2010 server user licensing model.
SharePoint Server should be license under two categories.
- Server License
- Client Access License (CAL)
Each SharePoint server in the farm should be license under SharePoint server license. Apart from the windows server licenses, SharePoint server should be licensed. This can be done when the time of installation of the SharePoint server.
The SQL servers in the SharePoint farm should be installed according to the SQL server licensing model.
Client Access License (CAL)
After that SharePoint farm should hold licenses for client access. These licenses are reviewed in the audit process and does not require any key in activation.
Depending on the user accessing organization requires to have CALs.
Intranet and Extranet CAL requirements
Assume organization setup a intranet and which is having users from internal AD , authentication providers. If all the user sources are with in the intranet and users are part of the organization; then each user needs a CAL to access the SharePoint server. CAL requirement is still valid for users who access the SharePoint server via internet.
Assume via authentication providers (Ex:- Membership Provider) , SharePoint is extended for Selected External Users (Named External Users) and Users are external and not part of the organization; thus no CAL is required for the user Access.
Internet CAL requirement
Assume SharePoint installation is as a public facing site and anonymous users are accessing the to view the content. thus these users does not require any CAL for accessing the content.
Reference : Microsoft