Disallow + in usernames.

myauth/models.py

@@ -7,10 +7,10 @@ from django.utils.translation import gettext_lazy as _
 
 @deconstructible
 class UnicodeUsernameValidator(validators.RegexValidator):
-    regex = r'^[\w.+-]+\Z'
+    regex = r'^[\w.-]+\Z'
     message = _(
         'Enter a valid username. This value may contain only letters, '
-        'numbers, and ./+/-/_ characters.'
+        'numbers, and ./-/_ characters.'
     )
     flags = 0
 
@@ -29,7 +29,7 @@ class User(AbstractUser):
         _('username'),
         max_length=150,
         unique=True,
-        help_text=_('Required. 150 characters or fewer. Letters, digits and ./+/-/_ only.'),
+        help_text=_('Required. 150 characters or fewer. Letters, digits and ./-/_ only.'),
         validators=[username_validator],
         error_messages={
             'unique': _("A user with that username already exists."),