List of settings
These settings can be used to configure how the user model
settings.AUTH_USER_MODEL) should be used.
You should add them as keys (with values)
USER_* fields can be set directly in the user class (specified
settings.AUTH_USER_MODEL) without using the
EMAIL_FIELD, etc.). These settings will override these provided in
Field used in verification, as part of signed data.
The given field should uniquely identify the user. This means that
using any user field which could change over time
username) is NOT recommended.