Thank you so much DisgruntledGoat.
When only Q2A is used, your method is vest answer at present. However, I use WordPress together, and should match user name with both systems. WordPress cannot use the double byte character for user name(I'm Japanese).
For security, I do not want to display user's property as much as possible. In that sense, input of full name(DisplayName/NickName) is also indispensable to me.