As @CBroe said, the field username
is no longer available in v2.0.
To request info for several Users at once via Graph API, you can use the following syntax:
GET /?ids={user_id_1},{user_id_2},{user_id_n}&fields={field_1},{field_1},{field_n}
Replace {field_n}
with the respective fields you want to get returned, and {user_id_n}
with the (app-specific) User IDs.