Setting the property on the login, provided it is before you have connected, will have the property passed to JDBC.
How are you setting the property in JDBC, are you just passing it as a property when you connect?
How have you configured JPA, are you using JDBC, or using a DataSource, perhaps include your persistence.xml. Normally the customizer would be in your persistence.xml.
Ensure you customizer is being called.
Note that if you have already connected your EntityManagerFactory, then customizing will not have any affect. I would guess that this is your problem.
Do you want to set the property one for the entire persistence
unit, or do you want to change it for each EntityManager? If it is per EntityManager, then you may need to use EclipseLink's session events, or EntityManager login properties.