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wiki:advanced:x2gobroker:start

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X2Go Session Broker

What is X2Go Session Broker

Most of you have already used X2Go Client in standalone mode. X2Go Client in standalone mode allows to be configured by the user himself. Normally, the user creates a set of session profiles that allow the user to work remotely on one or more X2Go Servers. See the documentation that explains the usage of X2Go Client.

When X2Go Client is run in broker mode, then it does not allow the local definition of session profiles. The list of session profiles gets provided by the X2Go Session Broker. A session broker is either a HTTP(s) server or an SSH server.

The implementations of the X2Go Session Broker can be manifold as long as the returned result is interpretable by X2Go Client.

How do I use an X2Go Session Broker with X2Go Client

If you have access to an X2Go Session Broker, you can launch X2Go Client in broker mode. There are several command line options to configure X2Go Client's broker mode

  • --broker-name=<name>: Name of broker to display in X2Go client. This parameter is optional
  • --broker-url=<protocol>://[username@]<host>[:port]/path: URL of broker. Protocol is “http”, “https” or “ssh”. You can specify an username in URL. In this case it will be pasted in authorization dialog of X2Go Client. URL examples are:
  • --broker-url=ssh:user@x2gobroker.org:22/usr/lib/x2go/x2gobroker.pl * --broker-ssh-key=<path to key>: Path to SSH key to use for authorization on broker. This parameter is valid only for SSH broker. * --broker-autologin: Use default SSH key or SSH agent for authorization on broker. This parameter is valid only for SSH broker. * --broker-noauth'': Do not ask for user credentials for broker authorizations. This can be useful if you using HTTP(S) broker without authentication. Username will be sent to broker if it specified in broker URL. This option is valid only for HTTP(S) broker. ===== How X2Go broker work ===== ==== Authentication ==== The X2Go client can use different methods of authentication. On HTTP(S) broker it could be username and password. On SSH broker a SSH key authentication can also be used. With both types of broker you can verify additional parameter “authid”. It is a user defined string which is saved in file. Path to file can be specified as X2Go Client command line option “–auth-id”. You can configure your broker not to check user data as it shown in example above. In such case function checkAccess should always return 1. In example of SSH-Broker this function is not called at all. The broker just print “Access granted” to let X2Go Client know, that authentication is successful. In some setups can make sense to give access to broker without authentication. For example in LAN if broker only serve as load balancer for X2Go Servers. 2.2. List of predefined X2Go sessions After successful authentication on broker, X2Go Client will request list of predefined X2Go Sessions. This list look just the same as session file of X2Go Client. The function, that send X2Go sessions to Client look like: <code> sub listSessions { print “START_USER_SESSIONS<br> <br>[ <session 1> ]<br> option1=value1<br> …. optionN=valueN<br> <br>[ <session 2> ]<br> option1=value1<br> …. optionN=valueN<br> END_USER_SESSIONS<br>”; } </code> The options are the same as in X2Go Client configuration file. There is only a difference in parameters “host” and “key”. And there are two parameters which are not supported in configuration file “status” and “usebrokerpass”. The “host” parameter it is not necessary a hostname of X2Go server. The actual address of a server will be provided after session selection. It can make sense in a case of load balancing. The best server will be chosen after selection and sent to client. The “key” parameter is also ignored. Key can be provided to client after selection of session too. However, you can set this parameter with some value to inform the Client, that passwordless authentication should be tried, for example: “key=will be provided later”. Parameter “usebrokerpass” say, that a user password for this session should not be asked, but broker password should be used instead. It can be useful if the broker and X2Go Server using same authentication server and there is no need to ask the same password twice. It is not recommended to use such authentication with HTTP Broker without SSL encryption. Parameter “status” can be one of two values “S” or “R”. It can be used to say X2Go Client that an instance (or instances) of this session already running or are suspended on server. X2Go Client will display the status on the Session button. 2.3. Selecting a session When predefined sessions are listed in X2Go Client, user can choose a session from sessions list. The id of chosen session will be sent to broker and broker send a connection data back to client. It is responsibility of function “selectSession”: <code> sub selectSession { my ($user, $sid)=@_; if($sid eq “123456789”) { print “SERVER:x2goserver.org:22\n”; } } </code> This function send a server address and SSH port for X2Go connection. If no other data are specified a new X2Go session will be created. Broker can also send to Client information, that suspended session should be resumed. In this case broker should also send a session data to Client: <code> sub selectSession { my ($user, $sid)=@_; if($sid eq “123456789”) { print “SERVER:phoca:22\n”; print “SESSION_INFO:12542|ncryer-53-1348753256_stDstartxfce4_dp24|53|debian|S|2012-09-27T06:40:57|7db77095d8a782f479d509d96f2e3261|188.195.168.12|30004|30005|2012-09-27T06:41:28|ncryer|285|30006|\n”; } </code> Broker can get this data from session database or by executing “x2golistsessions $user” on X2Go server. If X2Go Client running in broker mode, it will not verify if there are existing sessions on X2Go server. It is a responsibility of X2Go Broker. Broker should also suspend session before providing session data to client if session is running. The broker can also provide a SSH Key to client: <code> sub selectSession { my ($user, $sid)=@_; if($sid eq “123456789”) { print “SERVER:phoca:22\n”; print “—–BEGIN DSA PRIVATE KEY—– Proc-Type: 4,ENCRYPTED DEK-Info: AES-128-CBC,XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX yX7XLwCszCLM1FCYpdIGmM98vuHVcpNlVUBVgNcTxE1XCCnPZPjUXiNnUZPk1lme XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX o1q7Q1YmH43qI18lifjUhGZUTYWKQSsj2Am9bnjqaveV2aMEWymC8J9aJOYLpVZG XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX G1DwWnSRgyJaxRm4Ik0/kh78ioUfkVerXaCf2OKCMyiZBWcsNfvQwDa9MBrZ4rYW XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX VR60OGB7dHy+7ozqkjzuX+uB04GIqPJwG797i26Bo4v7uhbALjMa5qsObqXIPM1S XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX== —–END DSA PRIVATE KEY—–”; } } </code> It can be useful in some cases. It is recommended to transfer such keys only over encrypted channels. It is also recommended to transfer only temporary keys, which should be removed from known_hosts after authorization on X2Go server.
wiki/advanced/x2gobroker/start.1364400647.txt.gz · Last modified: 2013/03/27 16:10 by sunweaver