presto-session-property-managers/src/main/java/io/prestosql/plugin/session/db/DbSessionPropertyManager.java/DbSessionPropertyManager/getSystemSessionProperties
class DbSessionPropertyManager:    @Override
    public Map<String, String> getSystemSessionProperties(SessionConfigurationContext context)
    {
        List<SessionMatchSpec> sessionMatchSpecs = specsProvider.get();

        // later properties override earlier properties
        Map<String, String> combinedProperties = new HashMap<>();
        for (SessionMatchSpec sessionMatchSpec : sessionMatchSpecs) {
            combinedProperties.putAll(sessionMatchSpec.match(context));
        }

        return ImmutableMap.copyOf(combinedProperties);
    }