diff --git a/openedx/core/djangoapps/user_authn/views/login.py b/openedx/core/djangoapps/user_authn/views/login.py
index c9d8faed92..4bcc4226f3 100644
--- a/openedx/core/djangoapps/user_authn/views/login.py
+++ b/openedx/core/djangoapps/user_authn/views/login.py
@@ -483,7 +483,7 @@ def enterprise_selection_page(request, user, next_url):
 @ensure_csrf_cookie
 @require_http_methods(['POST'])
 @ratelimit(
-    key='openedx.core.djangoapps.util.ratelimit.request_post_email',
+    key='openedx.core.djangoapps.util.ratelimit.request_post_email_or_username',
     rate=settings.LOGISTRATION_PER_EMAIL_RATELIMIT_RATE,
     method='POST',
 )  # lint-amnesty, pylint: disable=too-many-statements
@@ -526,7 +526,7 @@ def login_user(request, api_version='v1'):  # pylint: disable=too-many-statement
     _parse_analytics_param_for_course_id(request)
 
     third_party_auth_requested = third_party_auth.is_enabled() and pipeline.running(request)
-    first_party_auth_requested = bool(request.POST.get('email')) or bool(request.POST.get('password'))
+    first_party_auth_requested = any(bool(request.POST.get(p)) for p in ['email', 'email_or_username', 'password'])
     is_user_third_party_authenticated = False
 
     set_custom_attribute('login_user_course_id', request.POST.get('course_id'))
diff --git a/openedx/core/djangoapps/user_authn/views/tests/test_login.py b/openedx/core/djangoapps/user_authn/views/tests/test_login.py
index e85611e996..a205362b3b 100644
--- a/openedx/core/djangoapps/user_authn/views/tests/test_login.py
+++ b/openedx/core/djangoapps/user_authn/views/tests/test_login.py
@@ -573,6 +573,24 @@ class LoginTest(SiteMixin, CacheIsolationTestCase, OpenEdxEventsTestMixin):
             response, _audit_log = self._login_response(self.user_email, 'wrong_password')
         self._assert_response(response, success=False, value='Too many failed login attempts')
 
+    @patch('openedx.core.djangoapps.util.ratelimit.real_ip')
+    def test_excessive_login_attempts_by_username(self, real_ip_mock):
+        # try logging in 6 times, the defalutlimit for the number of failed
+        # login attempts in one 5 minute period before the rate gets limited
+        # for a specific username.
+
+        # We freeze time to deal with the fact that rate limit time boundaries
+        # are not predictable and we don't want the test to be flaky.
+        with freeze_time():
+            for i in range(6):
+                password = f'test_password{i}'
+                # Provide unique IPs so we don't get ip rate limited.
+                real_ip_mock.return_value = f'192.168.1.{i}'
+                self._login_response(self.username, password)
+            # check to see if this response indicates that this was ratelimited
+            response, _audit_log = self._login_response(self.username, 'wrong_password')
+        self._assert_response(response, success=False, value='Too many failed login attempts')
+
     def test_excessive_login_attempts_by_ip(self):
         # try logging in 5 times, the default limit for the number of failed
         # login attempts in one 5 minute period before the rate gets limited
diff --git a/openedx/core/djangoapps/util/ratelimit.py b/openedx/core/djangoapps/util/ratelimit.py
index 8c1ee0f88d..a4ffec621c 100644
--- a/openedx/core/djangoapps/util/ratelimit.py
+++ b/openedx/core/djangoapps/util/ratelimit.py
@@ -52,3 +52,23 @@ def request_data_email(group, request) -> str:  # pylint: disable=unused-argumen
         email = str(uuid4())
 
     return email
+
+
+def request_post_email_or_username(group, request) -> str:  # pylint: disable=unused-argument
+    """
+    Return the the email or email_or_username post param if it exists, otherwise return a
+    random id.
+
+    If the request doesn't have an email or email_or_username post body param, treat it as
+    a unique key. This will probably mean that it will not get rate limited.
+
+    This ratelimit key function is meant to be used with the user_authn/views/login.py::login_user
+    function.  To rate-limit any first party auth.  For 3rd party auth, there is separate rate limiting
+    currently in place so we don't do any rate limiting for that case here.
+    """
+
+    email_or_username = request.POST.get('email_or_username') or request.POST.get('email')
+    if not email_or_username:
+        email_or_username = str(uuid4())
+
+    return email_or_username
diff --git a/openedx/core/djangoapps/util/tests/test_ratelimit.py b/openedx/core/djangoapps/util/tests/test_ratelimit.py
index 35be364ba1..0b60c9b068 100644
--- a/openedx/core/djangoapps/util/tests/test_ratelimit.py
+++ b/openedx/core/djangoapps/util/tests/test_ratelimit.py
@@ -46,3 +46,32 @@ class TestRateLimiting(TestCase):
         """
         XForwardedForMiddleware().process_request(self.request)
         assert ratelimit.real_ip(None, self.request) == '7.8.9.0'
+
+    def test_request_post_email(self):
+        """
+        Tests post email param.
+        """
+        expected_email = 'test@example.com'
+        self.request.POST = {'email': expected_email}
+        assert ratelimit.request_post_email(None, self.request) == expected_email
+
+    def test_request_data_email(self):
+        """
+        Tests data email param.
+        """
+        expected_email = 'test@example.com'
+        self.request.data = {'email': expected_email}
+        assert ratelimit.request_data_email(None, self.request) == expected_email
+
+    @ddt.data(
+        ('email', 'test@example.com'),
+        ('email_or_username', 'testUsername8967'),
+        ('email_or_username', 'testUsername@example.com')
+    )
+    @ddt.unpack
+    def test_request_post_email_or_username(self, param_name, expected_username_or_email):
+        """
+        Tests post email_or_username param.
+        """
+        self.request.POST = {param_name: expected_username_or_email}
+        assert ratelimit.request_post_email_or_username(None, self.request) == expected_username_or_email