Allow / character in username,password fields in _PROXY envvars. (#23973)

diff --git a/Lib/test/test_urllib2.py b/Lib/test/test_urllib2.py
index 12ad6ae..9db23e6 100644
--- a/Lib/test/test_urllib2.py
+++ b/Lib/test/test_urllib2.py
@@ -1851,9 +1851,17 @@ def test_parse_proxy(self):
              ('ftp', 'joe', 'password', 'proxy.example.com')),
             # Test for no trailing '/' case
             ('http://joe:password@proxy.example.com',
-             ('http', 'joe', 'password', 'proxy.example.com'))
+             ('http', 'joe', 'password', 'proxy.example.com')),
+            # Testcases with '/' character in username, password
+            ('http://user/name:password@localhost:22',
+             ('http', 'user/name', 'password', 'localhost:22')),
+            ('http://username:pass/word@localhost:22',
+             ('http', 'username', 'pass/word', 'localhost:22')),
+            ('http://user/name:pass/word@localhost:22',
+             ('http', 'user/name', 'pass/word', 'localhost:22')),
         ]
 
+
         for tc, expected in parse_proxy_test_cases:
             self.assertEqual(_parse_proxy(tc), expected)
 
diff --git a/Lib/urllib/request.py b/Lib/urllib/request.py
index 39974d9..e5febe6 100644
--- a/Lib/urllib/request.py
+++ b/Lib/urllib/request.py
@@ -773,7 +773,11 @@ def _parse_proxy(proxy):
             raise ValueError("proxy URL with no authority: %r" % proxy)
         # We have an authority, so for RFC 3986-compliant URLs (by ss 3.
         # and 3.3.), path is empty or starts with '/'
-        end = r_scheme.find("/", 2)
+        if '@' in r_scheme:
+            host_separator = r_scheme.find('@')
+            end = r_scheme.find("/", host_separator)
+        else:
+            end = r_scheme.find("/", 2)
         if end == -1:
             end = None
         authority = r_scheme[2:end]