In order to limit access to your website, we advise you to add a portal:
1. Go in the tab Manage > Event website > Website settings
2. Enable portal mode and select in the drop-down list the required field to access your website
3. Underneath, write a message to indicate which field your guests should insert
The guest will be able to write it either in upper or lowercase in the portal but this field should necessarily be written in lowercase in My Contacts tab.