Parameter `clients` in withAuthentication is unclear

[cchantep]

akka-http-pac4j/src/main/scala/com/stackstate/pac4j/AkkaHttpSecurity.scala

Line 129 in 5c1b2f1

def withAuthentication(clients: String = null /* Default null, meaning all defined clients */,

To what does it refer? For what I can see for know it depends on class name, e.g. if org.pac4j.saml.client.SAML2Client is configured clients must include SAML2Client (not the client ID on the SSO).