diff --git a/scrapy/downloadermiddlewares/httpauth.py b/scrapy/downloadermiddlewares/httpauth.py
index de5a81388..5228db786 100644
--- a/scrapy/downloadermiddlewares/httpauth.py
+++ b/scrapy/downloadermiddlewares/httpauth.py
@@ -3,13 +3,10 @@ HTTP basic auth downloader middleware
 
 See documentation in docs/topics/downloader-middleware.rst
 """
-import warnings
 
 from w3lib.http import basic_auth_header
 
 from scrapy import signals
-from scrapy.exceptions import ScrapyDeprecationWarning
-from scrapy.utils.httpobj import urlparse_cached
 from scrapy.utils.url import url_is_from_any_domain
 
 
@@ -28,25 +25,10 @@ class HttpAuthMiddleware:
         pwd = getattr(spider, "http_pass", "")
         if usr or pwd:
             self.auth = basic_auth_header(usr, pwd)
-            if not hasattr(spider, "http_auth_domain"):
-                warnings.warn(
-                    "Using HttpAuthMiddleware without http_auth_domain is deprecated and can cause security "
-                    "problems if the spider makes requests to several different domains. http_auth_domain "
-                    "will be set to the domain of the first request, please set it to the correct value "
-                    "explicitly.",
-                    category=ScrapyDeprecationWarning,
-                )
-                self.domain_unset = True
-            else:
-                self.domain = spider.http_auth_domain
-                self.domain_unset = False
+            self.domain = spider.http_auth_domain
 
     def process_request(self, request, spider):
         auth = getattr(self, "auth", None)
         if auth and b"Authorization" not in request.headers:
-            domain = urlparse_cached(request).hostname
-            if self.domain_unset:
-                self.domain = domain
-                self.domain_unset = False
             if not self.domain or url_is_from_any_domain(request.url, [self.domain]):
                 request.headers[b"Authorization"] = auth
diff --git a/tests/test_downloadermiddleware_httpauth.py b/tests/test_downloadermiddleware_httpauth.py
index 6b79234d0..fc110e6cc 100644
--- a/tests/test_downloadermiddleware_httpauth.py
+++ b/tests/test_downloadermiddleware_httpauth.py
@@ -1,10 +1,8 @@
 import unittest
 
-import pytest
 from w3lib.http import basic_auth_header
 
 from scrapy.downloadermiddlewares.httpauth import HttpAuthMiddleware
-from scrapy.exceptions import ScrapyDeprecationWarning
 from scrapy.http import Request
 from scrapy.spiders import Spider
 
@@ -31,39 +29,10 @@ class HttpAuthMiddlewareLegacyTest(unittest.TestCase):
         self.spider = TestSpiderLegacy("foo")
 
     def test_auth(self):
-        with pytest.warns(
-            ScrapyDeprecationWarning,
-            match="Using HttpAuthMiddleware without http_auth_domain is deprecated",
-        ):
+        with self.assertRaises(AttributeError):
             mw = HttpAuthMiddleware()
             mw.spider_opened(self.spider)
 
-        # initial request, sets the domain and sends the header
-        req = Request("http://example.com/")
-        assert mw.process_request(req, self.spider) is None
-        self.assertEqual(req.headers["Authorization"], basic_auth_header("foo", "bar"))
-
-        # subsequent request to the same domain, should send the header
-        req = Request("http://example.com/")
-        assert mw.process_request(req, self.spider) is None
-        self.assertEqual(req.headers["Authorization"], basic_auth_header("foo", "bar"))
-
-        # subsequent request to a different domain, shouldn't send the header
-        req = Request("http://example-noauth.com/")
-        assert mw.process_request(req, self.spider) is None
-        self.assertNotIn("Authorization", req.headers)
-
-    def test_auth_already_set(self):
-        with pytest.warns(
-            ScrapyDeprecationWarning,
-            match="Using HttpAuthMiddleware without http_auth_domain is deprecated",
-        ):
-            mw = HttpAuthMiddleware()
-            mw.spider_opened(self.spider)
-        req = Request("http://example.com/", headers=dict(Authorization="Digest 123"))
-        assert mw.process_request(req, self.spider) is None
-        self.assertEqual(req.headers["Authorization"], b"Digest 123")
-
 
 class HttpAuthMiddlewareTest(unittest.TestCase):
     def setUp(self):