diff --git a/Lib/test/test_urllib2.py b/Lib/test/test_urllib2.py

index 876fcd4..fe9a32b 100644

--- a/Lib/test/test_urllib2.py

+++ b/Lib/test/test_urllib2.py

@@ -1445,40 +1445,64 @@ class HandlerTests(unittest.TestCase):

         bypass = {'exclude_simple': True, 'exceptions': []}

         self.assertTrue(_proxy_bypass_macosx_sysconf('test', bypass))

-    def test_basic_auth(self, quote_char='"'):

-        opener = OpenerDirector()

-        password_manager = MockPasswordManager()

-        auth_handler = urllib.request.HTTPBasicAuthHandler(password_manager)

-        realm = "ACME Widget Store"

-        http_handler = MockHTTPHandler(

-            401, 'WWW-Authenticate: Basic realm=%s%s%s\r\n\r\n' %

-            (quote_char, realm, quote_char))

-        opener.add_handler(auth_handler)

-        opener.add_handler(http_handler)

-        self._test_basic_auth(opener, auth_handler, "Authorization",

-                              realm, http_handler, password_manager,

-                              "http://acme.example.com/protected",

-                              "http://acme.example.com/protected",

-                              )

-

-    def test_basic_auth_with_single_quoted_realm(self):

-        self.test_basic_auth(quote_char="'")

-

-    def test_basic_auth_with_unquoted_realm(self):

-        opener = OpenerDirector()

-        password_manager = MockPasswordManager()

-        auth_handler = urllib.request.HTTPBasicAuthHandler(password_manager)

-        realm = "ACME Widget Store"

-        http_handler = MockHTTPHandler(

-            401, 'WWW-Authenticate: Basic realm=%s\r\n\r\n' % realm)

-        opener.add_handler(auth_handler)

-        opener.add_handler(http_handler)

-        with self.assertWarns(UserWarning):

+    def check_basic_auth(self, headers, realm):

+        with self.subTest(realm=realm, headers=headers):

+            opener = OpenerDirector()

+            password_manager = MockPasswordManager()

+            auth_handler = urllib.request.HTTPBasicAuthHandler(password_manager)

+            body = '\r\n'.join(headers) + '\r\n\r\n'

+            http_handler = MockHTTPHandler(401, body)

+            opener.add_handler(auth_handler)

+            opener.add_handler(http_handler)

             self._test_basic_auth(opener, auth_handler, "Authorization",

-                                realm, http_handler, password_manager,

-                                "http://acme.example.com/protected",

-                                "http://acme.example.com/protected",

-                                )

+                                  realm, http_handler, password_manager,

+                                  "http://acme.example.com/protected",

+                                  "http://acme.example.com/protected")

+

+    def test_basic_auth(self):

+        realm = "realm2@example.com"

+        realm2 = "realm2@example.com"

+        basic = f'Basic realm="{realm}"'

+        basic2 = f'Basic realm="{realm2}"'

+        other_no_realm = 'Otherscheme xxx'

+        digest = (f'Digest realm="{realm2}", '

+                  f'qop="auth, auth-int", '

+                  f'nonce="dcd98b7102dd2f0e8b11d0f600bfb0c093", '

+                  f'opaque="5ccc069c403ebaf9f0171e9517f40e41"')

+        for realm_str in (

+            # test "quote" and 'quote'

+            f'Basic realm="{realm}"',

+            f"Basic realm='{realm}'",

+

+            # charset is ignored

+            f'Basic realm="{realm}", charset="UTF-8"',

+

+            # Multiple challenges per header

+            f'{basic}, {basic2}',

+            f'{basic}, {other_no_realm}',

+            f'{other_no_realm}, {basic}',

+            f'{basic}, {digest}',

+            f'{digest}, {basic}',

+        ):

+            headers = [f'WWW-Authenticate: {realm_str}']

+            self.check_basic_auth(headers, realm)

+

+        # no quote: expect a warning

+        with support.check_warnings(("Basic Auth Realm was unquoted",

+                                     UserWarning)):

+            headers = [f'WWW-Authenticate: Basic realm={realm}']

+            self.check_basic_auth(headers, realm)

+

+        # Multiple headers: one challenge per header.

+        # Use the first Basic realm.

+        for challenges in (

+            [basic,  basic2],

+            [basic,  digest],

+            [digest, basic],

+        ):

+            headers = [f'WWW-Authenticate: {challenge}'

+                       for challenge in challenges]

+            self.check_basic_auth(headers, realm)

     def test_proxy_basic_auth(self):

         opener = OpenerDirector()

diff --git a/Lib/urllib/request.py b/Lib/urllib/request.py

index c9945d9..6624e04 100644

--- a/Lib/urllib/request.py

+++ b/Lib/urllib/request.py

@@ -945,8 +945,15 @@ class AbstractBasicAuthHandler:

     # allow for double- and single-quoted realm values

     # (single quotes are a violation of the RFC, but appear in the wild)

-    rx = re.compile('(?:.*,)*[ \t]*([^ \t]+)[ \t]+'

-                    'realm=(["\']?)([^"\']*)\\2', re.I)

+    rx = re.compile('(?:^|,)'   # start of the string or ','

+                    '[ \t]*'    # optional whitespaces

+                    '([^ \t]+)' # scheme like "Basic"

+                    '[ \t]+'    # mandatory whitespaces

+                    # realm=xxx

+                    # realm='xxx'

+                    # realm="xxx"

+                    'realm=(["\']?)([^"\']*)\\2',

+                    re.I)

     # XXX could pre-emptively send auth info already accepted (RFC 2617,

     # end of section 2, and section 1.2 immediately after "credentials"

@@ -958,27 +965,51 @@ class AbstractBasicAuthHandler:

         self.passwd = password_mgr

         self.add_password = self.passwd.add_password

+    def _parse_realm(self, header):

+        # parse WWW-Authenticate header: accept multiple challenges per header

+        found_challenge = False

+        for mo in AbstractBasicAuthHandler.rx.finditer(header):

+            scheme, quote, realm = mo.groups()

+            if quote not in ['"', "'"]:

+                warnings.warn("Basic Auth Realm was unquoted",

+                              UserWarning, 3)

+

+            yield (scheme, realm)

+

+            found_challenge = True

+

+        if not found_challenge:

+            if header:

+                scheme = header.split()[0]

+            else:

+                scheme = ''

+            yield (scheme, None)

+

     def http_error_auth_reqed(self, authreq, host, req, headers):

         # host may be an authority (without userinfo) or a URL with an

         # authority

-        # XXX could be multiple headers

-        authreq = headers.get(authreq, None)

+        headers = headers.get_all(authreq)

+        if not headers:

+            # no header found

+            return

-        if authreq:

-            scheme = authreq.split()[0]

-            if scheme.lower() != 'basic':

-                raise ValueError("AbstractBasicAuthHandler does not"

-                                 " support the following scheme: '%s'" %

-                                 scheme)

-            else:

-                mo = AbstractBasicAuthHandler.rx.search(authreq)

-                if mo:

-                    scheme, quote, realm = mo.groups()

-                    if quote not in ['"',"'"]:

-                        warnings.warn("Basic Auth Realm was unquoted",

-                                      UserWarning, 2)

-                    if scheme.lower() == 'basic':

-                        return self.retry_http_basic_auth(host, req, realm)

+        unsupported = None

+        for header in headers:

+            for scheme, realm in self._parse_realm(header):

+                if scheme.lower() != 'basic':

+                    unsupported = scheme

+                    continue

+

+                if realm is not None:

+                    # Use the first matching Basic challenge.

+                    # Ignore following challenges even if they use the Basic

+                    # scheme.

+                    return self.retry_http_basic_auth(host, req, realm)

+

+        if unsupported is not None:

+            raise ValueError("AbstractBasicAuthHandler does not "

+                             "support the following scheme: %r"

+                             % (scheme,))

     def retry_http_basic_auth(self, host, req, realm):

         user, pw = self.passwd.find_user_password(realm, host)