Issue #19735: Implement private function ssl._create_stdlib_context() to

create SSLContext objects in Python's stdlib module. It provides a single
configuration point and makes use of SSLContext.load_default_certs().

11 files changed, 100 insertions, 55 deletions

diff --git a/Lib/asyncio/selector_events.py b/Lib/asyncio/selector_events.py
index 3efa4d2..14c9700 100644
--- a/Lib/asyncio/selector_events.py
+++ b/Lib/asyncio/selector_events.py
@@ -571,10 +571,8 @@ class _SelectorSslTransport(_SelectorTransport):
                 # context; in that case the sslcontext passed is None.
                 # The default is the same as used by urllib with
                 # cadefault=True.
-                sslcontext = ssl.SSLContext(ssl.PROTOCOL_SSLv23)
-                sslcontext.options |= ssl.OP_NO_SSLv2
-                sslcontext.set_default_verify_paths()
-                sslcontext.verify_mode = ssl.CERT_REQUIRED
+                sslcontext = ssl._create_stdlib_context(
+                    cert_reqs=ssl.CERT_REQUIRED)
 
         wrap_kwargs = {
             'server_side': server_side,
diff --git a/Lib/ftplib.py b/Lib/ftplib.py
index 9538fec..1b16e0a 100644
--- a/Lib/ftplib.py
+++ b/Lib/ftplib.py
@@ -727,6 +727,10 @@ else:
                                  "exclusive")
             self.keyfile = keyfile
             self.certfile = certfile
+            if context is None:
+                context = ssl._create_stdlib_context(self.ssl_version,
+                                                     certfile=certfile,
+                                                     keyfile=keyfile)
             self.context = context
             self._prot_p = False
             FTP.__init__(self, host, user, passwd, acct, timeout, source_address)
@@ -744,12 +748,7 @@ else:
                 resp = self.voidcmd('AUTH TLS')
             else:
                 resp = self.voidcmd('AUTH SSL')
-            if self.context is not None:
-                self.sock = self.context.wrap_socket(self.sock)
-            else:
-                self.sock = ssl.wrap_socket(self.sock, self.keyfile,
-                                            self.certfile,
-                                            ssl_version=self.ssl_version)
+            self.sock = self.context.wrap_socket(self.sock)
             self.file = self.sock.makefile(mode='r', encoding=self.encoding)
             return resp
 
@@ -788,11 +787,7 @@ else:
         def ntransfercmd(self, cmd, rest=None):
             conn, size = FTP.ntransfercmd(self, cmd, rest)
             if self._prot_p:
-                if self.context is not None:
-                    conn = self.context.wrap_socket(conn)
-                else:
-                    conn = ssl.wrap_socket(conn, self.keyfile, self.certfile,
-                                           ssl_version=self.ssl_version)
+                conn = self.context.wrap_socket(conn)
             return conn, size
 
         def abort(self):
diff --git a/Lib/http/client.py b/Lib/http/client.py
index 6e32c7b..5c52ba3 100644
--- a/Lib/http/client.py
+++ b/Lib/http/client.py
@@ -1179,9 +1179,7 @@ else:
             self.key_file = key_file
             self.cert_file = cert_file
             if context is None:
-                # Some reasonable defaults
-                context = ssl.SSLContext(ssl.PROTOCOL_SSLv23)
-                context.options |= ssl.OP_NO_SSLv2
+                context = ssl._create_stdlib_context()
             will_verify = context.verify_mode != ssl.CERT_NONE
             if check_hostname is None:
                 check_hostname = will_verify
diff --git a/Lib/imaplib.py b/Lib/imaplib.py
index b29487a..dabf161 100644
--- a/Lib/imaplib.py
+++ b/Lib/imaplib.py
@@ -742,9 +742,7 @@ class IMAP4:
             raise self.abort('TLS not supported by server')
         # Generate a default SSL context if none was passed.
         if ssl_context is None:
-            ssl_context = ssl.SSLContext(ssl.PROTOCOL_SSLv23)
-            # SSLv2 considered harmful.
-            ssl_context.options |= ssl.OP_NO_SSLv2
+            ssl_context = ssl._create_stdlib_context()
         typ, dat = self._simple_command(name)
         if typ == 'OK':
             self.sock = ssl_context.wrap_socket(self.sock)
@@ -1210,15 +1208,15 @@ if HAVE_SSL:
 
             self.keyfile = keyfile
             self.certfile = certfile
+            if ssl_context is None:
+                ssl_context = ssl._create_stdlib_context(certfile=certfile,
+                                                         keyfile=keyfile)
             self.ssl_context = ssl_context
             IMAP4.__init__(self, host, port)
 
         def _create_socket(self):
             sock = IMAP4._create_socket(self)
-            if self.ssl_context:
-                return self.ssl_context.wrap_socket(sock)
-            else:
-                return ssl.wrap_socket(sock, self.keyfile, self.certfile)
+            return self.ssl_context.wrap_socket(sock)
 
         def open(self, host='', port=IMAP4_SSL_PORT):
             """Setup connection to remote server on "host:port".
diff --git a/Lib/nntplib.py b/Lib/nntplib.py
index 9766be3..046f483 100644
--- a/Lib/nntplib.py
+++ b/Lib/nntplib.py
@@ -288,9 +288,7 @@ if _have_ssl:
         """
         # Generate a default SSL context if none was passed.
         if context is None:
-            context = ssl.SSLContext(ssl.PROTOCOL_SSLv23)
-            # SSLv2 considered harmful.
-            context.options |= ssl.OP_NO_SSLv2
+            context = ssl._create_stdlib_context()
         return context.wrap_socket(sock)
 
 
diff --git a/Lib/poplib.py b/Lib/poplib.py
index d68f169..00ffbcb 100644
--- a/Lib/poplib.py
+++ b/Lib/poplib.py
@@ -385,8 +385,7 @@ class POP3:
         if not 'STLS' in caps:
             raise error_proto('-ERR STLS not supported by server')
         if context is None:
-            context = ssl.SSLContext(ssl.PROTOCOL_SSLv23)
-            context.options |= ssl.OP_NO_SSLv2
+            context = ssl._create_stdlib_context()
         resp = self._shortcmd('STLS')
         self.sock = context.wrap_socket(self.sock)
         self.file = self.sock.makefile('rb')
@@ -421,15 +420,15 @@ if HAVE_SSL:
                                  "exclusive")
             self.keyfile = keyfile
             self.certfile = certfile
+            if context is None:
+                context = ssl._create_stdlib_context(certfile=certfile,
+                                                     keyfile=keyfile)
             self.context = context
             POP3.__init__(self, host, port, timeout)
 
         def _create_socket(self, timeout):
             sock = POP3._create_socket(self, timeout)
-            if self.context is not None:
-                sock = self.context.wrap_socket(sock)
-            else:
-                sock = ssl.wrap_socket(sock, self.keyfile, self.certfile)
+            sock = self.context.wrap_socket(sock)
             return sock
 
         def stls(self, keyfile=None, certfile=None, context=None):
diff --git a/Lib/smtplib.py b/Lib/smtplib.py
index 69ae845..6fc65f6 100644
--- a/Lib/smtplib.py
+++ b/Lib/smtplib.py
@@ -664,10 +664,10 @@ class SMTP:
             if context is not None and certfile is not None:
                 raise ValueError("context and certfile arguments are mutually "
                                  "exclusive")
-            if context is not None:
-                self.sock = context.wrap_socket(self.sock)
-            else:
-                self.sock = ssl.wrap_socket(self.sock, keyfile, certfile)
+            if context is None:
+                context = ssl._create_stdlib_context(certfile=certfile,
+                                                     keyfile=keyfile)
+            self.sock = context.wrap_socket(self.sock)
             self.file = None
             # RFC 3207:
             # The client MUST discard any knowledge obtained from
@@ -880,6 +880,9 @@ if _have_ssl:
                                  "exclusive")
             self.keyfile = keyfile
             self.certfile = certfile
+            if context is None:
+                context = ssl._create_stdlib_context(certfile=certfile,
+                                                     keyfile=keyfile)
             self.context = context
             SMTP.__init__(self, host, port, local_hostname, timeout,
                     source_address)
@@ -889,10 +892,7 @@ if _have_ssl:
                 print('connect:', (host, port), file=stderr)
             new_socket = socket.create_connection((host, port), timeout,
                     self.source_address)
-            if self.context is not None:
-                new_socket = self.context.wrap_socket(new_socket)
-            else:
-                new_socket = ssl.wrap_socket(new_socket, self.keyfile, self.certfile)
+            new_socket = self.context.wrap_socket(new_socket)
             return new_socket
 
     __all__.append("SMTP_SSL")
diff --git a/Lib/ssl.py b/Lib/ssl.py
index 880a3d4..72e6a6e 100644
--- a/Lib/ssl.py
+++ b/Lib/ssl.py
@@ -398,6 +398,43 @@ def create_default_context(purpose=Purpose.SERVER_AUTH, *, cafile=None,
     return context
 
 
+def _create_stdlib_context(protocol=PROTOCOL_SSLv23, *, cert_reqs=None,
+                           purpose=Purpose.SERVER_AUTH,
+                           certfile=None, keyfile=None,
+                           cafile=None, capath=None, cadata=None):
+    """Create a SSLContext object for Python stdlib modules
+
+    All Python stdlib modules shall use this function to create SSLContext
+    objects in order to keep common settings in one place. The configuration
+    is less restrict than create_default_context()'s to increase backward
+    compatibility.
+    """
+    if not isinstance(purpose, _ASN1Object):
+        raise TypeError(purpose)
+
+    context = SSLContext(protocol)
+    # SSLv2 considered harmful.
+    context.options |= OP_NO_SSLv2
+
+    if cert_reqs is not None:
+        context.verify_mode = cert_reqs
+
+    if keyfile and not certfile:
+        raise ValueError("certfile must be specified")
+    if certfile or keyfile:
+        context.load_cert_chain(certfile, keyfile)
+
+    # load CA root certs
+    if cafile or capath or cadata:
+        context.load_verify_locations(cafile, capath, cadata)
+    elif context.verify_mode != CERT_NONE:
+        # no explicit cafile, capath or cadata but the verify mode is
+        # CERT_OPTIONAL or CERT_REQUIRED. Let's try to load default system
+        # root CA certificates for the given purpose. This may fail silently.
+        context.load_default_certs(purpose)
+
+    return context
+
 class SSLSocket(socket):
     """This class implements a subtype of socket.socket that wraps
     the underlying OS socket in an SSL context when necessary, and
@@ -829,15 +866,16 @@ def get_server_certificate(addr, ssl_version=PROTOCOL_SSLv3, ca_certs=None):
     If 'ssl_version' is specified, use it in the connection attempt."""
 
     host, port = addr
-    if (ca_certs is not None):
+    if ca_certs is not None:
         cert_reqs = CERT_REQUIRED
     else:
         cert_reqs = CERT_NONE
-    s = create_connection(addr)
-    s = wrap_socket(s, ssl_version=ssl_version,
-                    cert_reqs=cert_reqs, ca_certs=ca_certs)
-    dercert = s.getpeercert(True)
-    s.close()
+    context = _create_stdlib_context(ssl_version,
+                                     cert_reqs=cert_reqs,
+                                     cafile=ca_certs)
+    with  create_connection(addr) as sock:
+        with context.wrap_socket(sock) as sslsock:
+            dercert = sslsock.getpeercert(True)
     return DER_cert_to_PEM_cert(dercert)
 
 def get_protocol_name(protocol_code):
diff --git a/Lib/test/test_ssl.py b/Lib/test/test_ssl.py
index 0b7ea47..afec72a 100644
--- a/Lib/test/test_ssl.py
+++ b/Lib/test/test_ssl.py
@@ -1018,6 +1018,27 @@ class ContextTests(unittest.TestCase):
         self.assertEqual(ctx.verify_mode, ssl.CERT_NONE)
         self.assertEqual(ctx.options & ssl.OP_NO_SSLv2, ssl.OP_NO_SSLv2)
 
+    def test__create_stdlib_context(self):
+        ctx = ssl._create_stdlib_context()
+        self.assertEqual(ctx.protocol, ssl.PROTOCOL_SSLv23)
+        self.assertEqual(ctx.verify_mode, ssl.CERT_NONE)
+        self.assertEqual(ctx.options & ssl.OP_NO_SSLv2, ssl.OP_NO_SSLv2)
+
+        ctx = ssl._create_stdlib_context(ssl.PROTOCOL_TLSv1)
+        self.assertEqual(ctx.protocol, ssl.PROTOCOL_TLSv1)
+        self.assertEqual(ctx.verify_mode, ssl.CERT_NONE)
+        self.assertEqual(ctx.options & ssl.OP_NO_SSLv2, ssl.OP_NO_SSLv2)
+
+        ctx = ssl._create_stdlib_context(ssl.PROTOCOL_TLSv1,
+                                         cert_reqs=ssl.CERT_REQUIRED)
+        self.assertEqual(ctx.protocol, ssl.PROTOCOL_TLSv1)
+        self.assertEqual(ctx.verify_mode, ssl.CERT_REQUIRED)
+        self.assertEqual(ctx.options & ssl.OP_NO_SSLv2, ssl.OP_NO_SSLv2)
+
+        ctx = ssl._create_stdlib_context(purpose=ssl.Purpose.CLIENT_AUTH)
+        self.assertEqual(ctx.protocol, ssl.PROTOCOL_SSLv23)
+        self.assertEqual(ctx.verify_mode, ssl.CERT_NONE)
+        self.assertEqual(ctx.options & ssl.OP_NO_SSLv2, ssl.OP_NO_SSLv2)
 
 
 class SSLErrorTests(unittest.TestCase):
diff --git a/Lib/urllib/request.py b/Lib/urllib/request.py
index bceb329..5995cbe 100644
--- a/Lib/urllib/request.py
+++ b/Lib/urllib/request.py
@@ -141,13 +141,9 @@ def urlopen(url, data=None, timeout=socket._GLOBAL_DEFAULT_TIMEOUT,
     if cafile or capath or cadefault:
         if not _have_ssl:
             raise ValueError('SSL support not available')
-        context = ssl.SSLContext(ssl.PROTOCOL_SSLv23)
-        context.options |= ssl.OP_NO_SSLv2
-        context.verify_mode = ssl.CERT_REQUIRED
-        if cafile or capath:
-            context.load_verify_locations(cafile, capath)
-        else:
-            context.set_default_verify_paths()
+        context = ssl._create_stdlib_context(cert_reqs=ssl.CERT_REQUIRED,
+                                             cafile=cafile,
+                                             capath=capath)
         https_handler = HTTPSHandler(context=context, check_hostname=True)
         opener = build_opener(https_handler)
     elif _opener is None:
diff --git a/Misc/NEWS b/Misc/NEWS
index 22d2c77..fc97d96 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -68,6 +68,10 @@ Core and Builtins
 Library
 -------
 
+- Issue #19735: Implement private function ssl._create_stdlib_context() to
+  create SSLContext objects in Python's stdlib module. It provides a single
+  configuration point and makes use of SSLContext.load_default_certs().
+
 - Issue #16203: Add re.fullmatch() function and regex.fullmatch() method,
   which anchor the pattern at both ends of the string to match.
   Original patch by Matthew Barnett.