The connection username's purpose is to establish a security check (a logical connection) before executing any GAM API call or piece of code. It's an additional security check that prevents GAM code from being executed unless a valid GAM connection exists. It's the same as having an API key.
Any number of connections can be defined for each GAM - Repository with the purpose of keeping the GAM database safe.
When you define a GAM Repository Connection you are asked to enter a Connection Username and a Connection User password.
That information has to be entered in the corresponding GeneXus properties if you want to connect using that GAM Repository connection.
It has a default value: <KB_name>, for prototyping purposes.
The default value of Connection Username property can be changed before the GAM database creation. In this case, a new GAM repository connection will be created during the GAM - Activation Process, and the connection user will have the settings given in the Connection Username property.
On the other hand, if the GAM database has already been created, only an existing connection username can be specified in the Connection Username property.
If the Connection Username property value changes, you need to build any object.
The connection.gam file is updated with the information given in the Connection Username property.