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See the License for the specific language governing permissions and limitations under the License. .. include:: ../../../common.defs .. highlight:: text .. default-domain:: cpp .. |Name| replace:: TLS Bridge |Name| ********** This plugin is used to provide TLS tunnels for connections between a Client and a Service via two gateway |TS| instances using explicit proxying. By configuring the |TS| instances the level of security in the tunnel can be easily controlled for all communications across the tunnels without having to update the client or service. Description =========== The tunnel is sustained by two instances of |TS|. .. uml:: :align: center hide empty members cloud "Cloud\nUntrusted\nNetworks" as Cloud node "Ingress ATS" node "Peer ATS" [Client] <--> [Ingress ATS] : Unsecure [Ingress ATS] <-> [Cloud] : Secure [Cloud] <-> [Peer ATS] : Secure [Peer ATS] <-u-> [Service] : Unsecure [Ingress ATS] ..> [tls_bridge\nPlugin] : Uses The ingress |TS| accepts an HTTP ``CONNECT`` request from the Client. This connection gets intercepted by the |Name| plugin inside |TS| if the destination matches one of the configured destinations. The plugin then makes a TLS connection to the peer |TS| using the configured level of security. The original ``CONNECT`` request from the Client to the ingress |TS| is then sent to the peer |TS| to create a connection from the peer |TS| to the Service. After this the Client has a virtual circuit to the Service and can use any TCP based communication (including TLS). Effectively the plugin causes the explicit proxy to work as if the Client had done the ``CONNECT`` directly to the peer |TS|. Note this means the DNS lookup for the Service is done by the peer |TS|, not the ingress |TS|. The plugin is configured with a mapping of Service names to peer |TS| instances. The Service names are URLs which will be in the original HTTP request made by the Client after connecting to the ingress |TS|. This means the FQDN for the Service is resolved in the environment of the peer |TS| and not the ingress |TS|. Configuration ============= |Name| requires at least two instances of |TS| (Ingress and Peer). The client connects to the ingress |TS|, and the peer |TS| connects to the service. The Peer could in theory be configured to connect on to a further |TS| instance, acting as the ingress to that peer, but that doesn't seem a useful case. #. Disable caching on |TS| in ``records.yaml``: .. code-block:: yaml :linenos: :emphasize-lines: 4 ts: http: cache: http: 0 #. Configure the ports. * The Peer |TS| must be listening on an SSL enabled proxy port. For instance, if the proxy port for the Peer is 4443, then configuration in ``records.yaml`` would have: .. code-block:: yaml :linenos: :emphasize-lines: 3 ts: http: server_ports: 4443:ssl * The Ingress |TS| must allow ``CONNECT`` to the Peer proxy port. This would be set in ``records.yaml`` by: .. code-block:: yaml :linenos: :emphasize-lines: 3 ts: http: connect_ports: 4443 The Ingress |TS| also needs ``proxy.config.http.server_ports`` configured to have proxy ports to which the Client can connect. #. By default |TS| requires remap in order to allow to outbound request to the peer. To disable this requirement and allow all connections, use the setting: .. code-block:: yaml :linenos: :emphasize-lines: 3 ts: url_remap: remap_required: 0 In this case |TS| will act as an open proxy which is unlikely to be a good idea. Therefore if this approach is used |TS| will need to run in a restricted environment or use access control (via ``ip_allow.yaml`` or ``iptables``). If this is unsuitable then an identity remap rule can be added for the peer |TS|. If the peer |TS| was named "peer.ats" and it listens on port 4443, then the remap rule would be :: map https://peer.ats:4443 https://peer.ats:4443 Remapping will be disabled for the user agent connection and so it will not need a rule. #. If remap is required on the peer to enable the outbound connection from the peer to the service (e.g. required remapping is not explicitly disabled) the destination port must be explicitly stated [#]_. E.g. :: map https://service:4443 https://service:4443 Note this remap rule cannot alter the actual HTTP transactions between the client and service because those happen inside what is effectively a tunnel between the client and service, supported by the two |TS| instances. This rule serves to allows the ``CONNECT`` sent from the ingress to cause a tunnel connection from the peer to the service. #. Configure the Ingress |TS| to verify the Peer server certificate: .. code-block:: yaml :linenos: :emphasize-lines: 6 ts: ssl: client: verify: server: policy: ENFORCED #. Configure Certificate Authority used by the Ingress |TS| to verify the Peer server certificate. If this is a directory, all of the certificates in the directory are treated as Certificate Authorities. .. code-block:: yaml :linenos: :emphasize-lines: 6 ts: ssl: client: CA: cert: filename: #. Configure the Ingress |TS| to provide a client certificate: .. code-block:: yaml :linenos: :emphasize-lines: 5-6 ts: ssl: client: cert: filename: path: #. Configure the Peer |TS| to verify the Ingress client certificate: .. code-block:: yaml :linenos: :emphasize-lines: 4 ts: ssl: client: certification_level: 2 #. Enable the |Name| plugin in ``plugin.config``. The plugin is configured by arguments in ``plugin.config``. These are arguments are in pairs of a *destination* and a *peer*. The destination is an anchored regular expression which is matched against the host name in the Client ``CONNECT``. The destinations are checked in order and the first match is used to select the peer |TS|. The peer should be an FQDN or IP address with an optional port. For the example above, if the Peer |TS| was named "peer.ats" on port 4443 and the Service at ``*.service.com``, the peer argument would be "peer.ats:4443". In ``plugin.config`` this would be:: tls_bridge.so .*[.]service[.]com peer.ats:4443 Note the '.' characters are escaped with brackets so that, for instance, "someservice.com" does not match the rule. If there was another service, "\*.altsvc.ats", via a different peer "altpeer.ats" on port 4443, the configuration would be :: tls_bridge.so .*[.]service[.]com peer.ats:4443 .*[.]altsvc.ats altpeer.ats:4443 Mappings can also be specified in an external file. For instance, if there was file named "bridge.config" in the default |TS| configuration directory which contained mappings, the ``plugin.config`` configuration line could look like :: tls_bridge.so .*[.]service[.]com peer.ats:4443 --file bridge.config or tls_bridge.so --file bridge.config .*[.]service[.]com peer.ats:4443 These are not identical - direct mappings and file mappings are processed in order. This means in the first example, the direct mapping is checked before any mapping in "bridge.config", and in the latter example the mappings in "bridge.config" are checked before the direct mappings. There can be multiple "--file" arguments, which are processed in the order they appear in "plugin.config". The file name can be absolute, or relative. If the file name is relative, it is relative to the |TS| configuration directory. Therefore, in these examples, "bridge.config" must be in the same directory as ``plugin.config``. The contents of "bridge.config" must be one mapping per line, with a regular expression separated by white space from the destination service. This is identical to the format in ``plugin.config`` except there is only one pair per line. E.g., valid content for "bridge.config" could be :: # Primary service location. .*[.]service[.]com peer.ats:4443 # Secondary. .*[.]altsvc.ats altpeer.ats:4443 Leading whitespace on a line is ignored, and if the first non-whitespace character is '#' then the entire line is ignored. Therefore if that is the content of "bridge.config", these two lines in "plugin.config" would behave identically :: tls_bridge.so --file bridge.config tls_bridge.so .*[.]service[.]com peer.ats:4443 .*[.]altsvc.ats altpeer.ats:4443 Notes ===== |Name| is distinct from more basic Layer 4 Routing available in |TS|. For the latter there is no intercept or change of the TLS exchange between the Client and the Service. The exchange looks like this .. uml:: :align: center actor Client participant "Ingress TS" as Ingress participant Service Client <-[#green]> Ingress : //TCP Connect// Client -[#blue]-> Ingress : TLS: ""CLIENT HELLO"" note over Ingress : Map SNI to upstream Service Ingress <-[#green]> Service : //TCP Connect// Ingress -[#blue]-> Service : TLS: ""CLIENT HELLO"" note right : Duplicate of data from Client. note over Ingress : Forward bytes between Client <&arrow-thick-left> <&arrow-thick-right> Service Client <--> Service The key points are * |TS| does no TLS negotiation at all. The properties of the connection between the Ingress |TS| and the Service are completely determined by the Client and Server negotiation. * No packets are modified, the ""CLIENT HELLO"" sent by the Ingress |TS| is an exact copy of that sent to the Ingress |TS| by the Client. It is only examined for the SNI data in order to select the Service. Implementation ============== The |Name| plugin uses :code:`TSHttpTxnIntercept` to gain control of the ingress Client session. If the session is valid then a separate connection to the peer |TS| is created using :code:`TSHttpConnect`. After the ingress |TS| connects to the peer |TS| it sends a duplicate of the Client ``CONNECT`` request. This is processed by the peer |TS| to connect to the Service. After this both |TS| instances then tunnel data between the Client and the Service, in effect becoming a transparent tunnel. The overall exchange looks like the following: .. uml:: :align: center @startuml box "Client Network" #DDFFDD actor Client entity "User Agent\nVConn" as lvc participant "Ingress ATS" as ingress entity "Upstream\nVConn" as rvc end box box "Corporate Network" #DDDDFF participant "Peer ATS" as peer database Service end box Client -> ingress : TCP or TLS connect activate lvc Client -> ingress : HTTP CONNECT ingress -> lvc : Intercept Transaction ingress -> peer : TLS connect activate rvc note over ingress,peer : Secure Tunnel ingress -> peer : HTTP CONNECT note over peer : DNS for Service is\ndone here. peer -> Service : TCP Connect note over Client, Service : At this point data can flow between the Client and Server\nover the secure link as a virtual connection, including any TLS handshake. Client <--> Service lvc <-> ingress : <&arrow-thick-left> Move data <&arrow-thick-right> ingress <-> rvc : <&arrow-thick-left> Move data <&arrow-thick-right> note over ingress : Plugin explicitly moves this data. @enduml A detailed view of the plugin operation. .. figure:: ../../../uml/images/TLS-Bridge-Plugin.svg :align: center A sequence diagram focusing on the request / response data flow. There is a :code:`NetVConn` for the connection to the Peer |TS| which is omitted for clarity. * Blue dotted lines are request or response data * Green lines are network connections. * Red lines are programmatic interactions. * Black lines are hook call backs. The :code:`200 OK` sent from the Peer |TS| is parsed and consumed by the plugin. An non-:code:`200` response means there was an error and the tunnel is shut down. To deal with the Client response clean up the response code is stored and used later during cleanup. .. figure:: ../../../uml/images/TLS-Bridge-Messages.svg :align: center A restartable state machine is used to recognize the end of the Peer |TS| response. The initial part of the response is easy because all that is needed is to wait until there is sufficient data for a minimal parse. The end can be an arbitrary distance in to the stream and may not all be in the same socket read. .. uml:: :align: center @startuml [*] -r> State_0 State_0 --> State_1 : CR State_1 --> State_0 : * State_1 --> State_1 : CR State_1 --> State_2 : LF State_2 --> State_3 : CR State_2 --> State_0 : * State_3 -r> [*] : LF State_3 --> State_1 : CR State_3 --> State_0 : * @enduml Debugging --------- Debugging messages for the plugin can be enabled with the "tls_bridge" debug tag. .. rubric:: Footnotes .. [#] This is likely due to a bug in |TS|, currently under investigation.