retrieving selected fields from a user object in a web-api

Hi all,

I am currently writing a web-api that will help integrate an external system with appian.  I want to write a function that returns selected fields from all the user objects in the system.  To that end, I have started writing a web-api that contains this key code:

local!allusers: a!forEach(
items: getdistinctusers(cons!IWMS_ALL_USERS_GROUP),
expression: {
firstName: user(fv!item.username, "firstName"),
lastName: user(fv!item.username, "lastName"),
email: user(fv!item.username, "email"),
phoneNumber: user(fv!item.username, "phoneOffice")
}
)

However, this fails with the error: "Expression evaluation error [evaluation ID = 5RH87KD4] at function a!forEach [line 24]: Error in a!forEach() expression during iteration 1: Expression evaluation error at function 'user' parameter 2 [line 27]: Invalid index: Cannot index property 'username' of type Text into type User"

If I code it as: 

local!allusers: a!forEach(
items: getdistinctusers(cons!IWMS_ALL_USERS_GROUP),
expression: fv!item
)

I get the json results as: [{ "id" : "LukeLiv" }, { "id" : "JamesLiv" }, { "id" : "EllaLiv" }, { "id" : "AvaFin" }, { "id" : "FredLiv" }]

What do I need to do in the expression to retrieve more fields than simply the id field in the returned json?

thanks heaps,

David