Context ctx = new InitialContext();
String userName = System.getProperty("user.name");
ctx.addToEnvironment(Context.SECURITY_PRINCIPAL, userName);

@Resource
EJBContext ctx;

// ...

String userName = ctx.getCallerPrincipal().getName();

java.lang.IllegalStateException: No valid security context for the caller identity
    at org.jboss.ejb3.EJBContextImpl.getCallerPrincipal(EJBContextImpl.java:143)

<application-policy name="simple">
    <authentication>
      <login-module code="org.jboss.security.auth.spi.SimpleServerLoginModule" flag="required" />
    </authentication>
  </application-policy>