User model field upenid_uid is optional.

openlobby/core/migrations/0009_auto_20180217_1850.py

+# Generated by Django 2.0.2 on 2018-02-17 17:50
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('core', '0008_loginattempt_openid_uid'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='user',
+            name='openid_uid',
+            field=models.CharField(max_length=255, null=True),
+        ),
+    ]

openlobby/core/models.py

@@ -10,7 +10,7 @@ class User(AbstractUser):
     """Custom user model. For simplicity we store OpenID 'sub' identifier in
     username field.
     """
-    openid_uid = models.CharField(max_length=255, unique=True, db_index=True)
+    openid_uid = models.CharField(max_length=255, null=True)
     extra = JSONField(null=True, blank=True)
     is_author = models.BooleanField(default=False)