The JCA container calls matchManagedConnections() in order to verify if a ManagedConnection can be reused - see http://docs.jboss.org/ironjacamar/userguide/1.1/en-US/html/samples.html#sample_helloworld_mcf. In most cases you would use the Subject and/or CRI to verify a match.
The ValidatingManagedConnectionFactory interface can be implemented in order to help the JCA container to clean up unneeded managed connections.
HTH