Add and implement --client-certificate option

Use a PEM certificate to authenticate HTTPS access to site

youtube_dl/__init__.py

@@ -320,6 +320,7 @@ def _real_main(argv=None):
         'password': opts.password,
         'twofactor': opts.twofactor,
         'videopassword': opts.videopassword,
+        'clientcertificate': opts.clientcertificate,
         'ap_mso': opts.ap_mso,
         'ap_username': opts.ap_username,
         'ap_password': opts.ap_password,

youtube_dl/options.py

@@ -370,6 +370,10 @@ def parseOpts(overrideArguments=None):
         '--video-password',
         dest='videopassword', metavar='PASSWORD',
         help='Video password (vimeo, youku)')
+    authentication.add_option(
+        '--client-certificate',
+        dest='clientcertificate', metavar='PATH',
+        help='Path to a single certificate file in PEM format, used to authenticate to the site')
 
     adobe_pass = optparse.OptionGroup(parser, 'Adobe Pass Options')
     adobe_pass.add_option(

youtube_dl/utils.py

@@ -2477,6 +2477,10 @@ def _create_http_connection(ydl_handler, http_class, is_https, *args, **kwargs):
     # https://github.com/ytdl-org/youtube-dl/issues/6727)
     if sys.version_info < (3, 0):
         kwargs['strict'] = True
+    if is_https:
+        client_cert_path = ydl_handler._params.get('clientcertificate')
+        if client_cert_path:
+            kwargs['cert_file'] = client_cert_path
     hc = http_class(*args, **compat_kwargs(kwargs))
     source_address = ydl_handler._params.get('source_address')