Grails 3 + Spring Security Core Plugin Confirm Password - grails

Question

Hello today I've started to learn Grails 3 with Spring Security Core Plugin but I'm having hard time with password Validation. When user is registering I want him to type password and confirmPassword. Everything would be ok if not hashing the password. I want my password to be encoded in database but with encoding I'm not able to compare those 2 passwords.
Here is my class:
#EqualsAndHashCode(includes='username')
#ToString(includes='username', includeNames=true, includePackage=false)
class User implements Serializable {
private static final long serialVersionUID = 1
transient springSecurityService
String username
String password
String confirmPass
boolean enabled = true
boolean accountExpired
boolean accountLocked
boolean passwordExpired
User(String username, String password) {
this()
this.username = username
this.password = password
this.confirmPass = password
}
Set<Role> getAuthorities() {
UserRole.findAllByUser(this)*.role
}
// because of that I can't compare password and confirmPass
def beforeInsert() {
encodePassword()
}
def beforeUpdate() {
if (isDirty('password')) {
encodePassword()
}
}
protected void encodePassword() {
password = springSecurityService?.passwordEncoder ? springSecurityService.encodePassword(password) : password
}
static transients = ['springSecurityService']
static constraints = {
username blank: false, unique: true
password blank: false, size: 5..60, password: true, display: false, validator: { val, obj ->
if (!obj.id && !obj.password) {
return 'validation.user.password' // my message
}
}
confirmPass blank: // now I'm stuck here, I've tried isPasswordValid() but won't work cuz of 'salt' What shout go here?
}
static mapping = {
password column: '`password`'
}
}
What should I do to make it working(valid both password are same and then encoded password store in database).