shiro验证时，当authenticationStrategy为AllSuccessfulStrategy时，如果某一个验证出错，那么
PrincipalCollection principalCollection = subject.getPrincipals();获得principalCollection为空值。
[main]
#指定securityManager的authenticator实现
authenticator=org.apache.shiro.authc.pam.ModularRealmAuthenticator
securityManager.authenticator=$authenticator #指定securityManager.authenticator的authenticationStrategy
allSuccessfulStrategy=org.apache.shiro.authc.pam.AllSuccessfulStrategy
securityManager.authenticator.authenticationStrategy=$allSuccessfulStrategy myRealm1=com.github.zhangkaitao.shiro.chapter2.realm.MyRealm1
myRealm2=com.github.zhangkaitao.shiro.chapter2.realm.MyRealm2
myRealm3=com.github.zhangkaitao.shiro.chapter2.realm.MyRealm3
securityManager.realms=$myRealm1,$myRealm3
