SSL client validation (certificate-based authentication)

docs/websockify.1

@@ -89,12 +89,27 @@ Here is an example of using websockify to wrap the vncserver command (which back
 
 `./websockify 5901 --wrap-mode=ignore -- vncserver -geometry 1024x768 :1`
 
-Here is an example of wrapping telnetd (from krb5-telnetd).telnetd exits after the connection closes so the wrap mode is set to respawn the command:
+Here is an example of wrapping telnetd (from krb5-telnetd). telnetd exits after the connection closes so the wrap mode is set to respawn the command:
 
 `sudo ./websockify 2023 --wrap-mode=respawn -- telnetd -debug 2023`
 
 The wstelnet.html page demonstrates a simple WebSockets based telnet client.
 
+.SS Use client certificate verification
+
+This feature requires Python 2.7.9 or newer or Python 3.4 or newer.
+
+The --verify-client option makes the server ask the client for a SSL certificate. Presenting a valid (not expired and trusted by any supplied certificate authority) certificate is required for the client connection. With -auth-plugin=ClientCertCNAuth, the client certificate can be checked against a list of authorised certificate users. Non-encrypted connection attempts always fail during authentication.
+
+Here is an example of a vncsevrer with password-less, certificate-driven authentication:
+
+`./websockify 5901 --cert=fullchain.pem --key=privkey.pem --ssl-only --verify-client --cafile=ca-certificates.crt --auth-plugin=ClientCertCNAuth --auth-source='[email protected] Joe User9824510' --web=noVNC/ --wrap-mode=ignore -- vncserver :1 -geometry 1024x768 -SecurityTypes=None`
+
+The --auth-source option takes a white-space separated list of common names. Depending on your clients certificates they can be verified email addresses, user-names or any other string used for identification.
+
+The --cafile option selects a file containing concatenated certificates of authorities trusted for validating clients. If this option is omitted, system default list of CAs is used. Upon connect, the client should supply the whole certificate chain. If your clients are known not to send intermediate certificates, they can be appended to the ca-file as well.
+
+Note: Most browsers ask the user to select a certificate only while connecting via HTTPS, not WebSockets. Connecting directly to the SSL secured WebSocket may cause the browser to abort the connection. If you want to connect via noVNC, the --web option should point to a copy of noVNC, so it is loaded from the same host.
 
 .SH AUTHOR
 Joel Martin ([email protected])

tests/test_websockifyserver.py

@@ -267,8 +267,25 @@ def fake_select(rlist, wlist, xlist, timeout=None):
         def fake_wrap_socket(*args, **kwargs):
             raise ssl.SSLError(ssl.SSL_ERROR_EOF)
 
+        class fake_create_default_context():
+            def __init__(self, purpose):
+                self.verify_mode = None
+            def load_cert_chain(self, certfile, keyfile):
+                pass
+            def set_default_verify_paths(self):
+                pass
+            def load_verify_locations(self, cafile):
+                pass
+            def wrap_socket(self, *args, **kwargs):
+                raise ssl.SSLError(ssl.SSL_ERROR_EOF)
+
         self.stubs.Set(select, 'select', fake_select)
-        self.stubs.Set(ssl, 'wrap_socket', fake_wrap_socket)
+        if (hasattr(ssl, 'create_default_context')):
+            # for recent versions of python
+            self.stubs.Set(ssl, 'create_default_context', fake_create_default_context)
+        else:
+            # for fallback for old versions of python
+            self.stubs.Set(ssl, 'wrap_socket', fake_wrap_socket)
         self.assertRaises(
             websockifyserver.WebSockifyServer.EClose, server.do_handshake,
             sock, '127.0.0.1')

websockify/auth_plugins.py

@@ -81,3 +81,23 @@ def authenticate(self, headers, target_host, target_port):
         origin = headers.get('Origin', None)
         if origin is None or origin not in self.source:
             raise InvalidOriginError(expected=self.source, actual=origin)
+
+class ClientCertCNAuth(object):
+    """Verifies client by SSL certificate. Specify src as whitespace separated list of common names."""
+
+    def __init__(self, src=None):
+        if src is None:
+            self.source = []
+        else:
+            self.source = src.split()
+
+    def authenticate(self, headers, target_host, target_port):
+        try:
+            if (headers.get('SSL_CLIENT_S_DN_CN') not in self.source):
+                raise AuthenticationError(response_code=403)
+        except AuthenticationError:
+            # re-raise AuthenticationError (raised by common name not in configured source list)
+            raise
+        except:
+            # deny access in case any error occurs (i.e. no data provided)
+            raise AuthenticationError(response_code=403)

websockify/websocketproxy.py

@@ -60,6 +60,20 @@ def validate_connection(self):
                 self.server.target_port = port
 
         if self.server.auth_plugin:
+
+            try:
+                # get client certificate data
+                client_cert_data = self.request.getpeercert()
+                # extract subject information
+                client_cert_subject = client_cert_data['subject']
+                # flatten data structure
+                client_cert_subject = dict([x[0] for x in client_cert_subject])
+                # add common name to headers (apache +StdEnvVars style)
+                self.headers['SSL_CLIENT_S_DN_CN'] = client_cert_subject['commonName']
+            except:
+                # not a SSL connection or client presented no certificate with valid data
+                pass
+
             try:
                 self.server.auth_plugin.authenticate(
                     headers=self.headers, target_host=self.server.target_host,
@@ -392,6 +406,13 @@ def websockify_init():
             help="disallow non-encrypted client connections")
     parser.add_option("--ssl-target", action="store_true",
             help="connect to SSL target as SSL client")
+    parser.add_option("--verify-client", action="store_true",
+            help="require encrypted client to present a valid certificate "
+            "(needs Python 2.7.9 or newer or Python 3.4 or newer)")
+    parser.add_option("--cafile", metavar="FILE",
+            help="file of concatenated certificates of authorities trusted "
+            "for validating clients (only effective with --verify-client). "
+            "If omitted, system default list of CAs is used.")
     parser.add_option("--unix-target",
             help="connect to unix socket target", metavar="FILE")
     parser.add_option("--inetd",

websockify/websockifyserver.py

@@ -319,6 +319,7 @@ class Terminate(Exception):
     def __init__(self, RequestHandlerClass, listen_fd=None,
             listen_host='', listen_port=None, source_is_ipv6=False,
             verbose=False, cert='', key='', ssl_only=None,
+            verify_client=False, cafile=None,
             daemon=False, record='', web='',
             file_only=False,
             run_once=False, timeout=0, idle_timeout=0, traffic=False,
@@ -333,6 +334,7 @@ def __init__(self, RequestHandlerClass, listen_fd=None,
         self.listen_port    = listen_port
         self.prefer_ipv6    = source_is_ipv6
         self.ssl_only       = ssl_only
+        self.verify_client  = verify_client
         self.daemon         = daemon
         self.run_once       = run_once
         self.timeout        = timeout
@@ -352,13 +354,15 @@ def __init__(self, RequestHandlerClass, listen_fd=None,
 
         # Make paths settings absolute
         self.cert = os.path.abspath(cert)
-        self.key = self.web = self.record = ''
+        self.key = self.web = self.record = self.cafile = ''
         if key:
             self.key = os.path.abspath(key)
         if web:
             self.web = os.path.abspath(web)
         if record:
             self.record = os.path.abspath(record)
+        if cafile:
+            self.cafile = os.path.abspath(cafile)
 
         if self.web:
             os.chdir(self.web)
@@ -518,7 +522,6 @@ def do_handshake(self, sock, address):
         """
         ready = select.select([sock], [], [], 3)[0]
 
-
         if not ready:
             raise self.EClose("ignoring socket not ready")
         # Peek, but do not read the data so that we have a opportunity
@@ -538,11 +541,31 @@ def do_handshake(self, sock, address):
                                   % self.cert)
             retsock = None
             try:
-                retsock = ssl.wrap_socket(
-                        sock,
-                        server_side=True,
-                        certfile=self.cert,
-                        keyfile=self.key)
+                try:
+                    # try creating new-style SSL wrapping for extended features
+                    context = ssl.create_default_context(ssl.Purpose.CLIENT_AUTH)
+                    context.load_cert_chain(certfile=self.cert, keyfile=self.key)
+                    if self.verify_client:
+                        context.verify_mode = ssl.CERT_REQUIRED
+                        context.set_default_verify_paths()
+                        if self.cafile:
+                            context.load_verify_locations(cafile=self.cafile)
+                    retsock = context.wrap_socket(
+                            sock,
+                            server_side=True)
+                except AttributeError as ae:
+                    if str(ae) != "'module' object has no attribute 'create_default_context'":
+                        # this exception is not caused by create_default_context not existing in old version. re-raise exception to be handled somewhere elese.
+                        raise
+                    elif self.verify_client:
+                        raise self.EClose("Client certificate verification requested, but not Python is too old.")
+                    else:
+                        # new-style SSL wrapping is not needed, falling back to old style
+                        retsock = ssl.wrap_socket(
+                                sock,
+                                server_side=True,
+                                certfile=self.cert,
+                                keyfile=self.key)
             except ssl.SSLError:
                 _, x, _ = sys.exc_info()
                 if x.args[0] == ssl.SSL_ERROR_EOF: