diff --git a/mellon/adapters.py b/mellon/adapters.py
index c11b679..09f569e 100644
--- a/mellon/adapters.py
+++ b/mellon/adapters.py
@@ -4,7 +4,7 @@ from django.core.exceptions import PermissionDenied
 from django.contrib import auth
 from django.contrib.auth.models import Group
 
-from . import utils, app_settings
+from . import utils, app_settings, models
 
 log = logging.getLogger(__name__)
 
@@ -47,17 +47,20 @@ class DefaultAdapter(object):
 
     def lookup_user(self, idp, saml_attributes):
         User = auth.get_user_model()
-        username = self.format_username(idp, saml_attributes)
-        if not username:
-            return None
-        provision = utils.get_setting(idp, 'PROVISION')
-        if provision:
-            user, created = User.objects.get_or_create(username=username)
-        else:
-            try:
-                user = User.objects.get(username=username)
-            except User.DoesNotExist:
-                return
+        name_id = saml_attributes['name_id_content']
+        issuer = saml_attributes['issuer']
+        try:
+            return User.objects.get(saml_identifiers__name_id=name_id,
+                    saml_identifiers__issuer=issuer)
+        except User.DoesNotExist:
+            if not utils.get_setting(idp, 'PROVISION'):
+                return None
+            username = self.format_username(idp, saml_attributes)
+            if not username:
+                return None
+            user = User(username=username)
+            user.save()
+            self.provision_name_id(user, idp, saml_attributes)
         return user
 
     def provision(self, user, idp, saml_attributes):
@@ -65,6 +68,12 @@ class DefaultAdapter(object):
         self.provision_superuser(user, idp, saml_attributes)
         self.provision_groups(user, idp, saml_attributes)
 
+    def provision_name_id(self, user, idp, saml_attributes):
+        models.UserSAMLIdentifier.objects.get_or_create(
+                user=user,
+                issuer=saml_attributes['issuer'],
+                name_id=saml_attributes['name_id_content'])
+
     def provision_attribute(self, user, idp, saml_attributes):
         realm = utils.get_setting(idp, 'REALM')
         attribute_mapping = utils.get_setting(idp, 'ATTRIBUTE_MAPPING')
diff --git a/mellon/migrations/0001_initial.py b/mellon/migrations/0001_initial.py
new file mode 100644
index 0000000..eca7a91
--- /dev/null
+++ b/mellon/migrations/0001_initial.py
@@ -0,0 +1,34 @@
+# -*- coding: utf-8 -*-
+from __future__ import unicode_literals
+
+from django.db import models, migrations
+from django.conf import settings
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        migrations.swappable_dependency(settings.AUTH_USER_MODEL),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name='UserSAMLIdentifier',
+            fields=[
+                ('id', models.AutoField(verbose_name='ID', serialize=False, auto_created=True, primary_key=True)),
+                ('issuer', models.TextField(verbose_name='Issuer')),
+                ('name_id', models.TextField(verbose_name='SAML identifier')),
+                ('created', models.DateTimeField(auto_now_add=True, verbose_name='created')),
+                ('user', models.ForeignKey(related_name='saml_identifiers', verbose_name='user', to=settings.AUTH_USER_MODEL)),
+            ],
+            options={
+                'verbose_name': 'user SAML identifier',
+                'verbose_name_plural': 'users SAML identifiers',
+            },
+            bases=(models.Model,),
+        ),
+        migrations.AlterUniqueTogether(
+            name='usersamlidentifier',
+            unique_together=set([('issuer', 'name_id')]),
+        ),
+    ]
diff --git a/mellon/models.py b/mellon/models.py
index 71a8362..7dfa1fa 100644
--- a/mellon/models.py
+++ b/mellon/models.py
@@ -1,3 +1,21 @@
 from django.db import models
+from django.utils.translation import ugettext_lazy as _
+from django.conf import settings
 
-# Create your models here.
+class UserSAMLIdentifier(models.Model):
+    user    = models.ForeignKey(
+                 verbose_name=_('user'),
+                 to=settings.AUTH_USER_MODEL,
+                 related_name='saml_identifiers')
+    issuer  = models.TextField(
+                 verbose_name=_('Issuer'))
+    name_id = models.TextField(
+                 verbose_name=_('SAML identifier'))
+    created = models.DateTimeField(
+                 verbose_name=_('created'),
+                 auto_now_add=True)
+
+    class Meta:
+        verbose_name = _('user SAML identifier')
+        verbose_name_plural = _('users SAML identifiers')
+        unique_together = (('issuer', 'name_id'),)