Fixed #19822 -- Added validation for uniqueness on USERNAME_FIELD on custom User models.

Thanks to Claude Peroz for the draft patch.

1 files changed, 4 insertions, 1 deletions

diff --git a/docs/topics/auth/customizing.txt b/docs/topics/auth/customizing.txt
index 7f1eff6624..d1ce6eb7dc 100644
--- a/docs/topics/auth/customizing.txt
+++ b/docs/topics/auth/customizing.txt
@@ -492,7 +492,10 @@ password resets. You must then provide some key implementation details:
         A string describing the name of the field on the User model that is
         used as the unique identifier. This will usually be a username of
         some kind, but it can also be an email address, or any other unique
-        identifier. In the following example, the field `identifier` is used
+        identifier. The field *must* be unique (i.e., have ``unique=True``
+        set in it's definition).
+
+        In the following example, the field `identifier` is used
         as the identifying field::
 
             class MyUser(AbstractBaseUser):