Issue #23857: Implement PEP 493

Adds a Python-2-only ssl module API and environment variable to
configure the default handling of SSL/TLS certificates for
HTTPS connections.

2 files changed, 73 insertions, 4 deletions

diff --git a/Lib/ssl.py b/Lib/ssl.py
index 34f7aaa..febc547 100644
--- a/Lib/ssl.py
+++ b/Lib/ssl.py
@@ -482,13 +482,30 @@ def _create_unverified_context(protocol=PROTOCOL_SSLv23, cert_reqs=None,
 
     return context
 
-# Used by http.client if no context is explicitly passed.
-_create_default_https_context = create_default_context
-
-
 # Backwards compatibility alias, even though it's not a public name.
 _create_stdlib_context = _create_unverified_context
 
+# PEP 493: Verify HTTPS by default, but allow envvar to override that
+_https_verify_envvar = 'PYTHONHTTPSVERIFY'
+
+def _get_https_context_factory():
+    if not sys.flags.ignore_environment:
+        config_setting = os.environ.get(_https_verify_envvar)
+        if config_setting == '0':
+            return _create_unverified_context
+    return create_default_context
+
+_create_default_https_context = _get_https_context_factory()
+
+# PEP 493: "private" API to configure HTTPS defaults without monkeypatching
+def _https_verify_certificates(enable=True):
+    """Verify server HTTPS certificates by default?"""
+    global _create_default_https_context
+    if enable:
+        _create_default_https_context = create_default_context
+    else:
+        _create_default_https_context = _create_unverified_context
+
 
 class SSLSocket(socket):
     """This class implements a subtype of socket.socket that wraps
diff --git a/Lib/test/test_ssl.py b/Lib/test/test_ssl.py
index e9723a7..86ba655 100644
--- a/Lib/test/test_ssl.py
+++ b/Lib/test/test_ssl.py
@@ -4,6 +4,7 @@
 import sys
 import unittest
 from test import test_support as support
+from test.script_helper import assert_python_ok
 import asyncore
 import socket
 import select
@@ -1174,6 +1175,57 @@ 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__https_verify_certificates(self):
+        # Unit test to check the contect factory mapping
+        # The factories themselves are tested above
+        # This test will fail by design if run under PYTHONHTTPSVERIFY=0
+        # (as will various test_httplib tests)
+
+        # Uses a fresh SSL module to avoid affecting the real one
+        local_ssl = support.import_fresh_module("ssl")
+        # Certificate verification is enabled by default
+        self.assertIs(local_ssl._create_default_https_context,
+                      local_ssl.create_default_context)
+        # Turn default verification off
+        local_ssl._https_verify_certificates(enable=False)
+        self.assertIs(local_ssl._create_default_https_context,
+                      local_ssl._create_unverified_context)
+        # And back on
+        local_ssl._https_verify_certificates(enable=True)
+        self.assertIs(local_ssl._create_default_https_context,
+                      local_ssl.create_default_context)
+        # The default behaviour is to enable
+        local_ssl._https_verify_certificates(enable=False)
+        local_ssl._https_verify_certificates()
+        self.assertIs(local_ssl._create_default_https_context,
+                      local_ssl.create_default_context)
+
+    def test__https_verify_envvar(self):
+        # Unit test to check the PYTHONHTTPSVERIFY handling
+        # Need to use a subprocess so it can still be run under -E
+        https_is_verified = """import ssl, sys; \
+            status = "Error: _create_default_https_context does not verify certs" \
+                       if ssl._create_default_https_context is \
+                          ssl._create_unverified_context \
+                     else None; \
+            sys.exit(status)"""
+        https_is_not_verified = """import ssl, sys; \
+            status = "Error: _create_default_https_context verifies certs" \
+                       if ssl._create_default_https_context is \
+                          ssl.create_default_context \
+                     else None; \
+            sys.exit(status)"""
+        extra_env = {}
+        # Omitting it leaves verification on
+        assert_python_ok("-c", https_is_verified, **extra_env)
+        # Setting it to zero turns verification off
+        extra_env[ssl._https_verify_envvar] = "0"
+        assert_python_ok("-c", https_is_not_verified, **extra_env)
+        # Any other value should also leave it on
+        for setting in ("", "1", "enabled", "foo"):
+            extra_env[ssl._https_verify_envvar] = setting
+            assert_python_ok("-c", https_is_verified, **extra_env)
+
     def test_check_hostname(self):
         ctx = ssl.SSLContext(ssl.PROTOCOL_TLSv1)
         self.assertFalse(ctx.check_hostname)