Can't configure standalone Jetty for hawtio authentication

[grgrzybek]

The instructions at https://hawt.io/docs/security.html#_jetty already mention problems with Jetty.

The problem is:

15:57:14 WARN {qtp191382150-33} : Login failed due to: java.lang.NullPointerException: Cannot invoke "org.eclipse.jetty.jaas.JAASLoginService.getBean(java.lang.Class)" because the return value of "java.lang.ThreadLocal.get()" is null
	at org.eclipse.jetty.jaas.spi.PropertyFileLoginModule.setupPropertyUserStore(PropertyFileLoginModule.java:71)
	at org.eclipse.jetty.jaas.spi.PropertyFileLoginModule.initialize(PropertyFileLoginModule.java:56)
	at java.base/javax.security.auth.login.LoginContext.invoke(LoginContext.java:745)
	at java.base/javax.security.auth.login.LoginContext$4.run(LoginContext.java:679)
	at java.base/javax.security.auth.login.LoginContext$4.run(LoginContext.java:677)
	at java.base/java.security.AccessController.doPrivileged(AccessController.java:712)
	at java.base/javax.security.auth.login.LoginContext.invokePriv(LoginContext.java:677)
	at java.base/javax.security.auth.login.LoginContext.login(LoginContext.java:587)
	at io.hawt.system.Authenticator.login(Authenticator.java:210)
	at io.hawt.system.Authenticator.doAuthenticate(Authenticator.java:184)
	at io.hawt.system.Authenticator.authenticate(Authenticator.java:155)
	at io.hawt.web.auth.LoginServlet.doPost(LoginServlet.java:68)
	at jakarta.servlet.http.HttpServlet.service(HttpServlet.java:520)
	at jakarta.servlet.http.HttpServlet.service(HttpServlet.java:587)
...

and the reason is that org.eclipse.jetty.jaas.spi.PropertyFileLoginModule requires a web application with proper <login-config>, while Hawtio has custom authentication.

It'd be nice to provide easy way for people who want to use Jetty.