This is because you are trying something which you should never do; allowing users to access the LOGIN USERNAME of a user.
Treat the Account data as sensitive as possible. Compare it with your passport with your social security number. You User/Name and User/Password are equally important and sensitive.
Always create a separated entity Person/Employee/Customer/…. with data which can be exchanged to other users. This entity should have a 1-1 association to account. when adding a person/Customer/…. the create also an account and associate.
This all has nothing to do with the Native part of your question. Its for both Native and Web app the same story