How is the [Origin] field set when a new case is created on the portal?

Question

How is the [Origin] field set when a new case is created on the portal?

Answer

The origin setup is executed in PortalCasePage of the following method:

setPortalColumnValues: function() {
    if (this.isAddMode() || this.isCopyMode()) {
        if (this.Terrasoft.SysValue.CURRENT_USER_ACCOUNT.value !== this.Terrasoft.GUID_EMPTY) {
            this.set("Account", this.Terrasoft.SysValue.CURRENT_USER_ACCOUNT);
        }
        this.set("Contact", this.Terrasoft.SysValue.CURRENT_USER_CONTACT);
        this.Terrasoft.SysSettings.querySysSettingsItem("PortalCaseOriginDef", function(value) {
            this.set("Origin", value);
        }, this);
        this.set("Owner", null);
    }
}

As you can see from the code, the field value is determined by the "PortalCaseOriginDef" system setting ("Default portal case source").