Since Java 8, the SaslServerFactory interface has been changed so that the serverName may be null. If null, the server name is considered "unbound" and the client can select what server name it wants to use.

The release notes say:

SASL service for multiple host names: When creating a SASL server, the server name can be set to null to denote an unbound server, which means a client can request for the service using any server name. After a context is established, the server can retrieve the name as a negotiated property with the key name SASL.BOUND_SERVER_NAME. See RFE 7110803.

The updated JavaDoc says:

serverName - The fully qualified host name of the server to authenticate to, or null if the server is not bound to any specific host name. If the mechanism does not allow an unbound server, a SaslException will be thrown.

The RFE link is: http://bugs.java.com/bugdatabase/view_bug.do?bug_id=7110803

The two SASL mechanisms in Elytron that would be impacted by this are DIGEST-MD5 and GSSAPI.