Mendix by default hadles the login. You first have to set your project security level to production.
For your games and attendees i would create the following domain model. Account already exist in the administration module. This way a user can attend to multiple games and a game can have multipe attendees.
You should be able to create a microflow where you create a attendee object which you link to the current users account and the game he wants to attend. Since this is basic mendix, I think its a good start to follow the different learning paths. YOu can find them on https://academy.mendix.com.
Maybe something like this?
- User Login
- Show a list of available games (Event) to select from
- a button “I will attend this game” – add them to the List of Attendees on click
As for ‘How can i say that that specific user (that logged in) clicked the attendance-button?’
You could either go with audit log from the app store or simply by checking ‘owner’ depending your need