The property exists related to Enable Integrated Security property.
It allows specifying a GUID which identifies a GAM - Repository.
Any valid GUID.
If you create a new knowledge base and configure Enable Integrated Security Property = Yes, one option is to create a new GAM repository and another one is to use an existing repository.
When creating a new Knowledge Base, GeneXus assigns a GUID by default to "Repository ID" property, but this value can be changed according to what you want to do: just create a new repository using the default GUID, create a new repository with a GUID generated by yourself, or use an existing repository.
So the cases would be:
a. Create a new GAM repository identified with this GUID.
You can use the default GUID value, or assign any valid GUID.
GeneXus checks in F5 (Build All) process if it's necessary to create GAM database tables. It connects to the database specified in GAM data store, and checks the existency of some tables and GAM version. If these tables don't exist, the GAM database tables are created with the Repository ID specified.
The GAM database will created and identified since now on, with this GUID.
b. Connect to an existing GAM database.
If you want to connect to an existing repository, and not to create a new one, you need to specify the corresponding Repository ID, and specify Administrator User Name, Administrator User Password, Connection User Name, Connection User Password of this GAM repository you want to connect to.
In the GAM data store properties you need to specify the corresponding database name, user name and password in order to connect to the database.
GeneXus Administration of GAM Repository
My first SD application with integrated security enabled
Enable Integrated Security property
Integrated Security Level property
Administrator User Password property
Connection User Name property
Connection User Password property
Login Object for Web property