bpo-41195: Add getter for Openssl security level (GH-21282)

Add an accessor under SSLContext.security_level as a wrapper around
SSL_CTX_get_security_level, see:
https://www.openssl.org/docs/manmaster/man3/SSL_CTX_get_security_level.html


------
This is my first time contributing, so please pull me up on all the things I missed or did incorrectly.

Automerge-Triggered-By: @tiran

Doc/library/ssl.rst

@@ -2032,6 +2032,16 @@ to speed up repeated connections from the same clients.
 
    .. versionadded:: 3.7
 
+.. attribute:: SSLContext.security_level
+
+   An integer representing the `security level
+   <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_get_security_level.html>`_
+   for the context. This attribute is read-only.
+
+   .. availability:: OpenSSL 1.1.0 or newer
+
+   .. versionadded:: 3.10
+
 .. attribute:: SSLContext.verify_flags
 
    The flags for certificate verification operations. You can set flags like

Lib/test/test_ssl.py

@@ -1270,6 +1270,25 @@ def test_min_max_version(self):
             ctx.maximum_version = ssl.TLSVersion.TLSv1
 
 
+    @unittest.skipUnless(
+        hasattr(ssl.SSLContext, 'security_level'),
+        "requires OpenSSL >= 1.1.0"
+    )
+    def test_security_level(self):
+        ctx = ssl.SSLContext()
+        # The default security callback allows for levels between 0-5
+        # with OpenSSL defaulting to 1, however some vendors override the
+        # default value (e.g. Debian defaults to 2)
+        security_level_range = {
+            0,
+            1, # OpenSSL default
+            2, # Debian
+            3,
+            4,
+            5,
+        }
+        self.assertIn(ctx.security_level, security_level_range)
+
     @unittest.skipUnless(have_verify_flags(),
                          "verify_flags need OpenSSL > 0.9.8")
     def test_verify_flags(self):

Misc/NEWS.d/next/Library/2020-07-02-15-03-04.bpo-41195.cEnpO3.rst

@@ -0,0 +1,2 @@
+Add read-only ssl.SSLContext.security_level attribute to retrieve the
+context's security level.

Modules/_ssl.c

@@ -3746,6 +3746,15 @@ PyDoc_STRVAR(PySSLContext_num_tickets_doc,
 "Control the number of TLSv1.3 session tickets");
 #endif /* OpenSSL 1.1.1 */
 
+#if (OPENSSL_VERSION_NUMBER >= 0x10100000L) && !defined(LIBRESSL_VERSION_NUMBER)
+static PyObject *
+get_security_level(PySSLContext *self, void *c)
+{
+    return PyLong_FromLong(SSL_CTX_get_security_level(self->ctx));
+}
+PyDoc_STRVAR(PySSLContext_security_level_doc, "The current security level");
+#endif /* OpenSSL 1.1.0 */
+
 static PyObject *
 get_options(PySSLContext *self, void *c)
 {
@@ -4793,6 +4802,10 @@ static PyGetSetDef context_getsetlist[] = {
                      (setter) set_verify_flags, NULL},
     {"verify_mode", (getter) get_verify_mode,
                     (setter) set_verify_mode, NULL},
+#if (OPENSSL_VERSION_NUMBER >= 0x10100000L) && !defined(LIBRESSL_VERSION_NUMBER)
+    {"security_level", (getter) get_security_level,
+                       NULL, PySSLContext_security_level_doc},
+#endif
     {NULL},            /* sentinel */
 };