diff --git a/src/djangooidc/backends.py b/src/djangooidc/backends.py
index 41e442f2d..38fde0ced 100644
--- a/src/djangooidc/backends.py
+++ b/src/djangooidc/backends.py
@@ -21,49 +21,66 @@ class OpenIdConnectBackend(ModelBackend):
     """
 
     def authenticate(self, request, **kwargs):
-        logger.debug("kwargs %s" % kwargs)
-        user = None
-        if not kwargs or "sub" not in kwargs.keys():
-            return user
+        logger.debug("kwargs %s", kwargs)
+
+        if not kwargs or "sub" not in kwargs:
+            return None
 
         UserModel = get_user_model()
         username = self.clean_username(kwargs["sub"])
+        openid_data = self.extract_openid_data(kwargs)
 
-        # Some OP may actually choose to withhold some information, so we must
-        # test if it is present
-        openid_data = {"last_login": timezone.now()}
-        openid_data["first_name"] = kwargs.get("given_name", "")
-        openid_data["last_name"] = kwargs.get("family_name", "")
-        openid_data["email"] = kwargs.get("email", "")
-        openid_data["phone"] = kwargs.get("phone", "")
-
-        # Note that this could be accomplished in one try-except clause, but
-        # instead we use get_or_create when creating unknown users since it has
-        # built-in safeguards for multiple threads.
         if getattr(settings, "OIDC_CREATE_UNKNOWN_USER", True):
-            args = {
-                UserModel.USERNAME_FIELD: username,
-                # defaults _will_ be updated, these are not fallbacks
-                "defaults": openid_data,
-            }
-
-            user, created = UserModel.objects.get_or_create(**args)
-
-            if not created:
-                # If user exists, update existing user
-                self.update_existing_user(user, args["defaults"])
-            else:
-                # If user is created, configure the user
-                user = self.configure_user(user, **kwargs)
+            user = self.get_or_create_user(UserModel, username, openid_data, kwargs)
         else:
-            try:
-                user = UserModel.objects.get_by_natural_key(username)
-            except UserModel.DoesNotExist:
-                return None
-        # run this callback for a each login
-        user.on_each_login()
+            user = self.get_user_by_username(UserModel, username)
+
+        if user:
+            user.on_each_login()
+
         return user
 
+    def extract_openid_data(self, kwargs):
+        """Extract OpenID data from authentication kwargs."""
+        return {
+            "last_login": timezone.now(),
+            "first_name": kwargs.get("given_name", ""),
+            "last_name": kwargs.get("family_name", ""),
+            "email": kwargs.get("email", ""),
+            "phone": kwargs.get("phone", ""),
+        }
+
+    def get_or_create_user(self, UserModel, username, openid_data, kwargs):
+        """Retrieve user by username or email, or create a new user."""
+        user = self.get_user_by_username(UserModel, username)
+
+        if not user and openid_data["email"]:
+            user = self.get_user_by_email(UserModel, openid_data["email"])
+            if user:
+                # if found by email, update the username
+                setattr(user, UserModel.USERNAME_FIELD, username)
+
+        if not user:
+            user = UserModel.objects.create(**{UserModel.USERNAME_FIELD: username}, **openid_data)
+            return self.configure_user(user, **kwargs)
+
+        self.update_existing_user(user, openid_data)
+        return user
+
+    def get_user_by_username(self, UserModel, username):
+        """Retrieve user by username."""
+        try:
+            return UserModel.objects.get(**{UserModel.USERNAME_FIELD: username})
+        except UserModel.DoesNotExist:
+            return None
+
+    def get_user_by_email(self, UserModel, email):
+        """Retrieve user by email."""
+        try:
+            return UserModel.objects.get(email=email)
+        except UserModel.DoesNotExist:
+            return None
+
     def update_existing_user(self, user, kwargs):
         """
         Update user fields without overwriting certain fields.
diff --git a/src/djangooidc/tests/test_backends.py b/src/djangooidc/tests/test_backends.py
index c15106fa9..4e8f80a23 100644
--- a/src/djangooidc/tests/test_backends.py
+++ b/src/djangooidc/tests/test_backends.py
@@ -1,5 +1,6 @@
 from django.test import TestCase
 from registrar.models import User
+from api.tests.common import less_console_noise_decorator
 from ..backends import OpenIdConnectBackend  # Adjust the import path based on your project structure
 
 
@@ -17,6 +18,7 @@ class OpenIdConnectBackendTestCase(TestCase):
     def tearDown(self) -> None:
         User.objects.all().delete()
 
+    @less_console_noise_decorator
     def test_authenticate_with_create_user(self):
         """Test that authenticate creates a new user if it does not find
         existing user"""
@@ -32,6 +34,7 @@ class OpenIdConnectBackendTestCase(TestCase):
         self.assertEqual(user.email, "john.doe@example.com")
         self.assertEqual(user.phone, "123456789")
 
+    @less_console_noise_decorator
     def test_authenticate_with_existing_user(self):
         """Test that authenticate updates an existing user if it finds one.
         For this test, given_name and family_name are supplied"""
@@ -50,6 +53,30 @@ class OpenIdConnectBackendTestCase(TestCase):
         self.assertEqual(user.email, "john.doe@example.com")
         self.assertEqual(user.phone, "123456789")
 
+    @less_console_noise_decorator
+    def test_authenticate_with_existing_user_same_email_different_username(self):
+        """Test that authenticate updates an existing user if it finds one.
+        In this case, match is to an existing record with matching email but
+        a non-matching username. The existing record's username should be udpated.
+        For this test, given_name and family_name are supplied"""
+        # Create an existing user with the same username
+        User.objects.create_user(username="old_username", email="john.doe@example.com")
+
+        # Ensure that the authenticate method updates the existing user
+        user = self.backend.authenticate(request=None, **self.kwargs)
+        self.assertIsNotNone(user)
+        self.assertIsInstance(user, User)
+
+        # Verify that user fields are correctly updated
+        self.assertEqual(user.first_name, "John")
+        self.assertEqual(user.last_name, "Doe")
+        self.assertEqual(user.email, "john.doe@example.com")
+        self.assertEqual(user.phone, "123456789")
+        self.assertEqual(user.username, "test_user")
+        # Assert that a user no longer exists by the old username
+        self.assertFalse(User.objects.filter(username="old_username").exists())
+
+    @less_console_noise_decorator
     def test_authenticate_with_existing_user_with_existing_first_last_phone(self):
         """Test that authenticate updates an existing user if it finds one.
         For this test, given_name and family_name are not supplied.
@@ -79,6 +106,7 @@ class OpenIdConnectBackendTestCase(TestCase):
         self.assertEqual(user.email, "john.doe@example.com")
         self.assertEqual(user.phone, "9999999999")
 
+    @less_console_noise_decorator
     def test_authenticate_with_existing_user_different_name_phone(self):
         """Test that authenticate updates an existing user if it finds one.
         For this test, given_name and family_name are supplied and overwrite"""
@@ -100,6 +128,7 @@ class OpenIdConnectBackendTestCase(TestCase):
         self.assertEqual(user.email, "john.doe@example.com")
         self.assertEqual(user.phone, "123456789")
 
+    @less_console_noise_decorator
     def test_authenticate_with_unknown_user(self):
         """Test that authenticate returns None when no kwargs are supplied"""
         # Ensure that the authenticate method handles the case when the user is not found
diff --git a/src/registrar/assets/src/sass/_theme/_typography.scss b/src/registrar/assets/src/sass/_theme/_typography.scss
index 75d5170e8..22069f726 100644
--- a/src/registrar/assets/src/sass/_theme/_typography.scss
+++ b/src/registrar/assets/src/sass/_theme/_typography.scss
@@ -11,7 +11,8 @@ address,
 }
 
 h1:not(.usa-alert__heading),
-h2:not(.usa-alert__heading),
+// .module h2 excludes headers in DJA
+h2:not(.usa-alert__heading, .module h2),
 h3:not(.usa-alert__heading),
 h4:not(.usa-alert__heading),
 h5:not(.usa-alert__heading),
diff --git a/src/registrar/fixtures/fixtures_users.py b/src/registrar/fixtures/fixtures_users.py
index f1623e674..977bf0858 100644
--- a/src/registrar/fixtures/fixtures_users.py
+++ b/src/registrar/fixtures/fixtures_users.py
@@ -352,12 +352,37 @@ class UserFixture:
 
     @staticmethod
     def _get_existing_users(users):
+        # if users match existing users in db by email address, update the users with the username
+        # from the db. this will prevent duplicate users (with same email) from being added to db.
+        # it is ok to keep the old username in the db because the username will be updated by oidc process during login
+
+        # Extract email addresses from users
+        emails = [user.get("email") for user in users]
+
+        # Fetch existing users by email
+        existing_users_by_email = User.objects.filter(email__in=emails).values_list("email", "username", "id")
+
+        # Create a dictionary to map emails to existing usernames
+        email_to_existing_user = {user[0]: user[1] for user in existing_users_by_email}
+
+        # Update the users list with the usernames from existing users by email
+        for user in users:
+            email = user.get("email")
+            if email and email in email_to_existing_user:
+                user["username"] = email_to_existing_user[email]  # Update username with the existing one
+
+        # Get the user identifiers (username, id) for the existing users to query the database
         user_identifiers = [(user.get("username"), user.get("id")) for user in users]
+
+        # Fetch existing users by username or id
         existing_users = User.objects.filter(
             username__in=[user[0] for user in user_identifiers] + [user[1] for user in user_identifiers]
         ).values_list("username", "id")
+
+        # Create sets for usernames and ids that exist
         existing_usernames = set(user[0] for user in existing_users)
         existing_user_ids = set(user[1] for user in existing_users)
+
         return existing_usernames, existing_user_ids
 
     @staticmethod