authentication (optional) is the required level of authentication; valid values are:
none specifies that no authentication is required at all
guest specifies that at least guest authentication is required
user specifies that at least named user authentication is required
admin specifies that at least a named admin authentication is required
Note 1: if not specified, the default value is none Note 2: The optional runas attribute can be used to force the execution of a web script as a specific user. This can only be specified for web scripts that are stored in the Java Class path.
Look carefully to note 2: you can set an authentication level on the execution of the webscript, but you can decide that certain part of it can be executed as another user. Moreover you can also extend the access levels to nodes modifying the permissionDefinitions.xml under WEB_INF/classes/alfresco/model in order to have your custom security level for a user, other that Coordinator, Collaborator, etc. It depends on what you need…
Didn't take long to work out that it looks to be rather involved and likely impractical. The authentication value options are coded in an enum (Description.RequiredAuthentication) that is used in numerous places…making it very difficult to add a new one.