OpenVPN Management Interface Notes
 ----------------------------------
 
 The OpenVPN Management interface allows OpenVPN to
 be administratively controlled from an external program via

 a TCP or unix domain socket.

 The interface has been specifically designed for developers
 who would like to programmatically or remotely control
 an OpenVPN daemon, and can be used when OpenVPN is running
 as a client or server.

 
 The management interface is implemented using a client/server TCP

 connection or unix domain socket where OpenVPN will listen on a
 provided IP address and port for incoming management client connections.

 
 The management protocol is currently cleartext without an explicit
 security layer.  For this reason, it is recommended that the

 management interface either listen on a unix domain socket,
 localhost (127.0.0.1), or on the local VPN address.  It's possible
 to remotely connect to the management interface over the VPN itself,
 though some capabilities will be limited in this mode, such as the
 ability to provide private key passwords.

 
 The management interface is enabled in the OpenVPN

 configuration file using the following directive:

 
 --management
 

 See the man page for documentation on this and related
 directives.

 
 Once OpenVPN has started with the management layer enabled,
 you can telnet to the management port (make sure to use
 a telnet client which understands "raw" mode).
 
 Once connected to the management port, you can use
 the "help" command to list all commands.
 

 COMMAND -- bytecount
 --------------------
 
 The bytecount command is used to request real-time notification
 of OpenVPN bandwidth usage.
 
 Command syntax:
 
   bytecount n (where n > 0) -- set up automatic notification of
                                bandwidth usage once every n seconds
   bytecount 0 -- turn off bytecount notifications
 
 If OpenVPN is running as a client, the bytecount notification
 will look like this:
 
   >BYTECOUNT:{BYTES_IN},{BYTES_OUT}
 
 BYTES_IN is the number of bytes that have been received from
 the server and BYTES_OUT is the number of bytes that have been
 sent to the server.
 
 If OpenVPN is running as a server, the bytecount notification
 will look like this:
 
   >BYTECOUNT_CLI:{CID},{BYTES_IN},{BYTES_OUT}
  
 CID is the Client ID, BYTES_IN is the number of bytes that have
 been received from the client and BYTES_OUT is the number of
 bytes that have been sent to the client.
 
 Note that when the bytecount command is used on the server, every
 connected client will report its bandwidth numbers once every n
 seconds.
 
 When the client disconnects, the final bandwidth numbers will be
 placed in the 'bytes_received' and 'bytes_sent' environmental variables
 as included in the >CLIENT:DISCONNECT notification.
 

 COMMAND -- echo
 ---------------
 
 The echo capability is used to allow GUI-specific
 parameters to be either embedded in the OpenVPN config file
 or pushed to an OpenVPN client from a server.
 
 Command examples:
 
   echo on      -- turn on real-time notification of echo messages
   echo all     -- print the current echo history list
   echo off     -- turn off real-time notification of echo messages
   echo on all  -- atomically enable real-time notification,
                   plus show any messages in history buffer
 
 For example, suppose you are developing a OpenVPN GUI and
 you want to give the OpenVPN server the ability to ask
 the GUI to forget any saved passwords.
 
 In the OpenVPN server config file, add:
 
   push "echo forget-passwords"
 
 When the OpenVPN client receives its pulled list of directives
 from the server, the "echo forget-passwords" directive will
 be in the list, and it will cause the management interface
 to save the "forget-passwords" string in its list of echo
 parameters.
 
 The management client can use "echo all" to output the full
 list of echoed parameters, "echo on" to turn on real-time
 notification of echoed parameters via the ">ECHO:" prefix,
 or "echo off" to turn off real-time notification.
 
 When the GUI connects to the OpenVPN management socket, it
 can issue an "echo all" command, which would produce output
 like this:
 
   1101519562,forget-passwords
   END
 
 Essentially the echo command allowed us to pass parameters from
 the OpenVPN server to the OpenVPN client, and then to the
 management client (such as a GUI).  The large integer is the
 unix date/time when the echo parameter was received.
 
 If the management client had issued the command "echo on",
 it would have enabled real-time notifications of echo
 parameters.  In this case, our "forget-passwords" message
 would be output like this:
 
   >ECHO:1101519562,forget-passwords
 
 Like the log command, the echo command can atomically show
 history while simultaneously activating real-time updates:
 
   echo on all
 
 The size of the echo buffer is currently hardcoded to 100
 messages.
 
 COMMAND -- exit, quit
 ---------------------
 
 Close the managment session, and resume listening on the
 management port for connections from other clients. Currently,
 the OpenVPN daemon can at most support a single management client
 any one time.
 
 COMMAND -- help
 ---------------
 
 Print a summary of commands.
 
 COMMAND -- hold
 ---------------
 
 The hold command can be used to manipulate the hold flag,
 or release OpenVPN from a hold state.
 
 If the hold flag is set on initial startup or
 restart, OpenVPN will hibernate prior to initializing
 the tunnel until the management interface receives
 a "hold release" command.
 
 The --management-hold directive of OpenVPN can be used
 to start OpenVPN with the hold flag set.
 
 The hold flag setting is persistent and will not
 be reset by restarts.
 
 OpenVPN will indicate that it is in a hold state by
 sending a real-time notification to the management
 client:
 
   >HOLD:Waiting for hold release
 
 Command examples:
 
   hold         -- show current hold flag, 0=off, 1=on.
   hold on      -- turn on hold flag so that future restarts
                   will hold.
   hold off     -- turn off hold flag so that future restarts will
                   not hold.
   hold release -- leave hold state and start OpenVPN, but
                   do not alter the current hold flag setting.
 
 COMMAND -- kill
 ---------------
 
 In server mode, kill a particlar client instance.
 
 Command examples:
 
   kill Test-Client -- kill the client instance having a
                       common name of "Test-Client".
   kill 1.2.3.4:4000 -- kill the client instance having a
                        source address and port of 1.2.3.4:4000
 
 Use the "status" command to see which clients are connected.
 
 COMMAND -- log
 --------------
 
 Show the OpenVPN log file.  Only the most recent n lines
 of the log file are cached by the management interface, where
 n is controlled by the OpenVPN --management-log-cache directive.
 
 Command examples:
 
   log on     -- Enable real-time output of log messages.
   log all    -- Show currently cached log file history.
   log on all -- Atomically show all currently cached log file
                 history then enable real-time notification of
                 new log file messages.
   log off    -- Turn off real-time notification of log messages.
   log 20     -- Show the most recent 20 lines of log file history.
 
 Real-time notification format:
 
 Real-time log messages begin with the ">LOG:" prefix followed
 by the following comma-separated fields:
 
   (a) unix integer date/time,
   (b) zero or more message flags in a single string:
       I -- informational
       F -- fatal error
       N -- non-fatal error
       W -- warning
       D -- debug, and
   (c) message text.
 
 COMMAND -- mute
 ---------------
 
 Change the OpenVPN --mute parameter.  The mute parameter is
 used to silence repeating messages of the same message
 category.
 
 Command examples:
 
   mute 40 -- change the mute parameter to 40
   mute    -- show the current mute setting
 
 COMMAND -- net
 --------------
 
 (Windows Only) Produce output equivalent to the OpenVPN
 --show-net directive.  The output includes OpenVPN's view
 of the system network adapter list and routing table based
 on information returned by the Windows IP helper API.
 

 COMMAND -- pid
 --------------
 
 Shows the process ID of the current OpenVPN process.
 

 COMMAND -- password and username
 --------------------------------
 
   The password command is used to pass passwords to OpenVPN.
 
   If OpenVPN is run with the --management-query-passwords
   directive, it will query the management interface for RSA
   private key passwords and the --auth-user-pass
   username/password.
 
   When OpenVPN needs a password from the management interface,
   it will produce a real-time ">PASSWORD:" message.
 
   Example 1:
 
     >PASSWORD:Need 'Private Key' password
 
   OpenVPN is indicating that it needs a password of type
   "Private Key".
 
   The management client should respond to this query as follows:
 
     password "Private Key" foo
 
   Example 2:
 
     >PASSWORD:Need 'Auth' username/password
 
   OpenVPN needs a --auth-user-pass password.  The management
   client should respond:
 
     username "Auth" foo
     password "Auth" bar
 
   The username/password itself can be in quotes, and special
   characters such as double quote or backslash must be escaped,
   for example,
 
     password "Private Key" "foo\"bar"
 
   The escaping rules are the same as for the config file.
   See the "Command Parsing" section below for more info.
 
   The PASSWORD real-time message type can also be used to
   indicate password or other types of authentication failure:
 
   Example 3: The private key password is incorrect and OpenVPN
   is exiting:
 
     >PASSWORD:Verification Failed: 'Private Key'
 
   Example 4: The --auth-user-pass username/password failed,
   and OpenVPN is exiting:
 
     >PASSWORD:Verification Failed: 'Auth'
 

   Example 5: The --auth-user-pass username/password failed,
   and the server provided a custom client-reason-text string
   using the client-deny server-side management interface command.
 
     >PASSWORD:Verification Failed: 'custom server-generated string'
 

 COMMAND -- forget-passwords
 ---------------------------
 
 The forget-passwords command will cause the daemon to forget passwords
 entered during the session.
 
 Command example:
 
   forget-passwords -- forget passwords entered so far.
 

 COMMAND -- signal
 -----------------
 
 The signal command will send a signal to the OpenVPN daemon.
 The signal can be one of SIGHUP, SIGTERM, SIGUSR1, or SIGUSR2.
 
 Command example:
 
   signal SIGUSR1 -- send a SIGUSR1 signal to daemon
 
 COMMAND -- state
 ----------------
 
 Show the current OpenVPN state, show state history, or
 enable real-time notification of state changes.
 
 These are the OpenVPN states:
 
 CONNECTING    -- OpenVPN's initial state.
 WAIT          -- (Client only) Waiting for initial response
                  from server.
 AUTH          -- (Client only) Authenticating with server.
 GET_CONFIG    -- (Client only) Downloading configuration options
                  from server.
 ASSIGN_IP     -- Assigning IP address to virtual network
                  interface.
 ADD_ROUTES    -- Adding routes to system.
 CONNECTED     -- Initialization Sequence Completed.
 RECONNECTING  -- A restart has occurred.
 EXITING       -- A graceful exit is in progress.
 
 Command examples:
 
   state        -- Print current OpenVPN state.
   state on     -- Enable real-time notification of state changes.
   state off    -- Disable real-time notification of state changes.
   state all    -- Print current state history.
   state 3      -- Print the 3 most recent state transitions.
   state on all -- Atomically show state history while at the
                   same time enable real-time state notification
 		  of future state transitions.
 
 The output format consists of 4 comma-separated parameters: 
   (a) the integer unix date/time,
   (b) the state name,
   (c) optional descriptive string (used mostly on RECONNECTING

       and EXITING to show the reason for the disconnect),

   (d) optional TUN/TAP local IP address (shown for ASSIGN_IP

       and CONNECTED), and
   (e) optional address of remote server (OpenVPN 2.1 or higher).

 
 Real-time state notifications will have a ">STATE:" prefix
 prepended to them.
 
 COMMAND -- status
 -----------------
 
 Show current daemon status information, in the same format as
 that produced by the OpenVPN --status directive.
 
 Command examples:
 
 status   -- Show status information using the default status
             format version.
 

 status 3 -- Show status information using the format of
             --status-version 3.

 
 COMMAND -- username
 -------------------
 
 See the "password" section above.
 
 COMMAND -- verb
 ---------------
 
 Change the OpenVPN --verb parameter.  The verb parameter
 controls the output verbosity, and may range from 0 (no output)
 to 15 (maximum output).  See the OpenVPN man page for additional
 info on verbosity levels.
 
 Command examples:
 
   verb 4  -- change the verb parameter to 4
   mute    -- show the current verb setting
 
 COMMAND -- version
 ------------------
 
 Show the current OpenVPN and Management Interface versions.
 
 
 COMMAND -- auth-retry
 ---------------------
 
 Set the --auth-retry setting to control how OpenVPN responds to
 username/password authentication errors.  See the manual page
 for more info.
 
 Command examples:
 
   auth-retry interact -- Don't exit when bad username/passwords are entered.
                          Query for new input and retry.
 

 COMMAND -- needok  (OpenVPN 2.1 or higher)

 ------------------------------------------

 
 Confirm a ">NEED-OK" real-time notification, normally used by
 OpenVPN to block while waiting for a specific user action.
 
 Example:
 
   OpenVPN needs the user to insert a cryptographic token,
   so it sends a real-time notification:
 
     >NEED-OK:Need 'token-insertion-request' confirmation MSG:Please insert your cryptographic token
 
   The management client, if it is a GUI, can flash a dialog
   box containing the text after the "MSG:" marker to the user.
   When the user acknowledges the dialog box,
   the management client can issue this command:
 
      needok token-insertion-request ok
   or
      needok token-insertion-request cancel
 

 COMMAND -- needstr  (OpenVPN 2.1 or higher)
 -------------------------------------------
 
 Confirm a ">NEED-STR" real-time notification, normally used by
 OpenVPN to block while waiting for a specific user input.
 
 Example:
 
   OpenVPN needs the user to specify some input, so it sends a
   real-time notification:
 
     >NEED-STR:Need 'name' input MSG:Please specify your name
 
   The management client, if it is a GUI, can flash a dialog
   box containing the text after the "MSG:" marker to the user.
   When the user acknowledges the dialog box,
   the management client can issue this command:
 
      needstr name "John"
 
 COMMAND -- pkcs11-id-count  (OpenVPN 2.1 or higher)
 ---------------------------------------------------
 
 Retrieve available number of certificates.
 
 Example:
 
      pkcs11-id-count
      >PKCS11ID-COUNT:5
 
 COMMAND -- pkcs11-id-get  (OpenVPN 2.1 or higher)
 -------------------------------------------------
 
 Retrieve certificate by index, the ID string should be provided
 as PKCS#11 identity, the blob is BASE64 encoded certificate.
 
 Example:
 
      pkcs11-id-get 1
      PKCS11ID-ENTRY:'1', ID:'<snip>', BLOB:'<snip>'
 

 COMMAND -- client-auth  (OpenVPN 2.1 or higher)
 -----------------------------------------------
 
 Authorize a ">CLIENT:CONNECT" or ">CLIENT:REAUTH" request and specify
 "client-connect" configuration directives in a subsequent text block.
 
 The OpenVPN server should have been started with the
 --management-client-auth directive so that it will ask the management
 interface to approve client connections.
 
 
   client-auth {CID} {KID}
   line_1
   line_2
   ...
   line_n
   END
 
 CID,KID -- client ID and Key ID.  See documentation for ">CLIENT:"
 notification for more info.
 
 line_1 to line_n -- client-connect configuration text block, as would be
 returned by a --client-connect script.  The text block may be null, with
 "END" immediately following the "client-auth" line (using a null text
 block is equivalent to using the client-auth-nt command).
 
 A client-connect configuration text block contains OpenVPN directives
 that will be applied to the client instance object representing a newly
 connected client.
 
 COMMAND -- client-auth-nt  (OpenVPN 2.1 or higher)
 --------------------------------------------------
 
 Authorize a ">CLIENT:CONNECT" or ">CLIENT:REAUTH" request without specifying
 client-connect configuration text.
 
 The OpenVPN server should have been started with the
 --management-client-auth directive so that it will ask the management
 interface to approve client connections.
 
   client-auth-nt {CID} {KID}
 
 CID,KID -- client ID and Key ID.  See documentation for ">CLIENT:"
 notification for more info.
 
 COMMAND -- client-deny  (OpenVPN 2.1 or higher)
 -----------------------------------------------
 
 Deny a ">CLIENT:CONNECT" or ">CLIENT:REAUTH" request.
 

   client-deny {CID} {KID} "reason-text" ["client-reason-text"]

 
 CID,KID -- client ID and Key ID.  See documentation for ">CLIENT:"
 notification for more info.
 
 reason-text: a human-readable message explaining why the authentication
 request was denied.  This message will be output to the OpenVPN log
 file or syslog.
 

 client-reason-text: a message that will be sent to the client as
 part of the AUTH_FAILED message.
 

 Note that client-deny denies a specific Key ID (pertaining to a
 TLS renegotiation).  A client-deny command issued in response to
 an initial TLS key negotiation (notified by ">CLIENT:CONNECT") will
 terminate the client session after returning "AUTH-FAILED" to the client.
 On the other hand, a client-deny command issued in response to
 a TLS renegotiation (">CLIENT:REAUTH") will invalidate the renegotiated
 key, however the TLS session associated with the currently active
 key will continue to live for up to --tran-window seconds before
 expiration.
 
 To immediately kill a client session, use "client-kill".
 
 COMMAND -- client-kill  (OpenVPN 2.1 or higher)
 -----------------------------------------------
 
 Immediately kill a client instance by CID.
 
   client-kill {CID}
 
 CID -- client ID.  See documentation for ">CLIENT:" notification for more
 info.
 
 COMMAND -- client-pf  (OpenVPN 2.1 or higher)
 ---------------------------------------------
 
 Push a packet filter file to a specific client.
 
 The OpenVPN server should have been started with the
 --management-client-pf directive so that it will require that
 VPN tunnel packets sent or received by client instances must
 conform to that client's packet filter configuration.
 
   client-pf {CID}
   line_1
   line_2
   ...
   line_n
   END
 
 CID -- client ID.  See documentation for ">CLIENT:" notification for
 more info.
 
 line_1 to line_n -- the packet filter configuration file for this
 client.
 
 Packet filter file grammar:
 
  [CLIENTS DROP|ACCEPT]
  {+|-}common_name1
  {+|-}common_name2
  . . .
  [SUBNETS DROP|ACCEPT]
  {+|-}subnet1
  {+|-}subnet2
  . . .
  [END]
 
  Subnet: IP-ADDRESS | IP-ADDRESS/NUM_NETWORK_BITS | "unknown"
 
  CLIENTS refers to the set of clients (by their common-name) which
  this instance is allowed ('+') to connect to, or is excluded ('-')
  from connecting to.  Note that in the case of client-to-client
  connections, such communication must be allowed by the packet filter
  configuration files of both clients AND the --client-to-client
  directive must have been specified in the OpenVPN server config.
 
  SUBNETS refers to IP addresses or IP address subnets which this
  client instance may connect to ('+') or is excluded ('-') from
  connecting to, and applies to IPv4 and ARP packets.  The special
  "unknown" tag refers to packets of unknown type, i.e. a packet that
  is not IPv4 or ARP.
 
  DROP or ACCEPT defines default policy when there is no explicit match
  for a common-name or subnet.  The [END] tag must exist.
 
  Notes:
 
  * The SUBNETS section currently only supports IPv4 addresses and
    subnets.
 
  * A given client or subnet rule applies to both incoming and
    outgoing packets.
 
  * The CLIENTS list is order-invariant.  Because the list is stored
    as a hash-table, the order of the list does not affect its function.
 
  * The SUBNETS table is scanned sequentially, and the first item to
    match is chosen.  Therefore the SUBNETS table is NOT order-invariant.
 
  * No client-to-client communication is allowed unless the
    --client-to-client configuration directive is enabled AND
    the CLIENTS list of BOTH clients allows the communication.
 
 Example packet filter spec, as transmitted to the management interface:
 
  client-pf 42
  [CLIENTS ACCEPT]
  -accounting
  -enigma
  [SUBNETS DROP]
  -10.46.79.9
  +10.0.0.0/8
  [END]
  END
 
 The above example sets the packet filter policy for the client
 identified by CID=42.  This client may connect to all other clients
 except those having a common name of "accounting" or "enigma".
 The client may only interact with external IP addresses in the
 10.0.0.0/8 subnet, however access to 10.46.79.9 is specifically
 excluded.
 
 Another example packet filter spec, as transmitted to the
 management interface:
 
  client-pf 99
  [CLIENTS DENY]
  +public
  [SUBNETS ACCEPT]
  +10.10.0.1
  -10.0.0.0/8
  -unknown
  [END]
  END
 
 The above example sets the packet filter policy for the client
 identified by CID=99.  This client may not connect to any other
 clients except those having a common name of "public".  It may
 interact with any external IP address except those in the
 10.0.0.0/8 netblock.  However interaction with one address in
 the 10.0.0.0/8 netblock is allowed: 10.10.0.1.  Also, the client
 may not interact with external IP addresses using an "unknown"
 protocol (i.e. one that is not IPv4 or ARP).
 

 COMMAND -- remote  (OpenVPN AS 2.1.5/OpenVPN 2.3 or higher)

 --------------------------------------------
 
 Provide remote host/port in response to a >REMOTE notification
 (client only).  Requires that the --management-query-remote
 directive is used.
 
   remote ACTION [HOST PORT]
 
 The "remote" command should only be given in response to a >REMOTE
 notification.  For example, the following >REMOTE notification
 indicates that the client config file would ordinarily connect
 to vpn.example.com port 1194 (UDP):
 
   >REMOTE:vpn.example.com,1194,udp
 
 Now, suppose we want to override the host and port, connecting
 instead to vpn.otherexample.com port 1234.  After receiving
 the above notification, use this command:
 
   remote MOD vpn.otherexample.com 1234
 
 To accept the same host and port as the client would ordinarily
 have connected to, use this command:
 
   remote ACCEPT
 
 To skip the current connection entry and advance to the next one,
 use this command:
 
   remote SKIP
 

 COMMAND -- proxy  (OpenVPN 2.3 or higher)
 --------------------------------------------
 
 Provide proxy server host/port and flags in response to a >PROXY
 notification (client only).  Requires that the --management-query-proxy
 directive is used.
 
   proxy TYPE HOST PORT ["nct"]
 
 The "proxy" command must only be given in response to a >PROXY
 notification.  Use the "nct" flag if you only want to allow
 non-cleartext auth with the proxy server.  The following >PROXY
 notification indicates that the client config file would ordinarily
 connect to the first --remote configured, vpn.example.com using TCP:
 
   >PROXY:1,TCP,vpn.example.com
 
 Now, suppose we want to connect to the remote host using the proxy server
 proxy.intranet port 8080 with secure authentication only, if required.
 After receiving the above notification, use this command:
 
   proxy HTTP proxy.intranet 8080 nct
 
 You can also use the SOCKS keyword to pass a SOCKS server address, like:
 
   proxy SOCKS fe00::1 1080
 
 To accept connecting to the host and port directly, use this command:
 
   proxy NONE
 

 OUTPUT FORMAT
 -------------
 
 (1) Command success/failure indicated by "SUCCESS: [text]" or
     "ERROR: [text]".
 
 (2) For commands which print multiple lines of output,
     the last line will be "END".
 
 (3) Real-time messages will be in the form ">[source]:[text]",

     where source is "CLIENT", "ECHO", "FATAL", "HOLD", "INFO", "LOG",

     "NEED-OK", "PASSWORD", or "STATE".

 
 REAL-TIME MESSAGE FORMAT
 ------------------------
 
 The OpenVPN management interface produces two kinds of
 output: (a) output from a command, or (b) asynchronous,
 real-time output which can be generated at any time.
 
 Real-time messages start with a '>' character in the first
 column and are immediately followed by a type keyword
 indicating the type of real-time message.  The following
 types are currently defined:
 

 BYTECOUNT -- Real-time bandwidth usage notification, as enabled
              by "bytecount" command when OpenVPN is running as
              a client.
 
 BYTECOUNT_CLI -- Real-time bandwidth usage notification per-client,
 	         as enabled by "bytecount" command when OpenVPN is
                  running as a server.
 

 CLIENT   -- Notification of client connections and disconnections
             on an OpenVPN server.  Enabled when OpenVPN is started
             with the --management-client-auth option.  CLIENT
             notifications may be multi-line.  See "The CLIENT
             notification" section below for detailed info.
 

 ECHO     -- Echo messages as controlled by the "echo" command.
 
 FATAL    -- A fatal error which is output to the log file just
             prior to OpenVPN exiting.
 
 HOLD     -- Used to indicate that OpenVPN is in a holding state
             and will not start until it receives a
             "hold release" command.
 
 INFO     -- Informational messages such as the welcome message.
 
 LOG      -- Log message output as controlled by the "log" command.
 

 NEED-OK  -- OpenVPN needs the end user to do something, such as
             insert a cryptographic token.  The "needok" command can
             be used to tell OpenVPN to continue.
 

 NEED-STR -- OpenVPN needs information from end, such as
             a certificate to use.  The "needstr" command can
             be used to tell OpenVPN to continue.
 

 PASSWORD -- Used to tell the management client that OpenVPN
             needs a password, also to indicate password
             verification failure.
 
 STATE    -- Shows the current OpenVPN state, as controlled
             by the "state" command.
 

 The CLIENT notification
 -----------------------
 
 The ">CLIENT:" notification is enabled by the --management-client-auth
 OpenVPN configuration directive that gives the management interface client
 the responsibility to authenticate OpenVPN clients after their client
 certificate has been verified.  CLIENT notifications may be multi-line, and
 the sequentiality of a given CLIENT notification, its associated environmental
 variables, and the terminating ">CLIENT:ENV,END" line are guaranteed to be
 atomic.
 
 CLIENT notification types:
 
 (1) Notify new client connection ("CONNECT") or existing client TLS session
     renegotiation ("REAUTH").  Information about the client is provided
     by a list of environmental variables which are documented in the OpenVPN
     man page.  The environmental variables passed are equivalent to those
     that would be passed to an --auth-user-pass-verify script.
 
     >CLIENT:CONNECT|REAUTH,{CID},{KID}
     >CLIENT:ENV,name1=val1
     >CLIENT:ENV,name2=val2
     >CLIENT:ENV,...
     >CLIENT:ENV,END
 

 (2) Notify successful client authentication and session initiation.
     Called after CONNECT.
 
     >CLIENT:ESTABLISHED,{CID}
     >CLIENT:ENV,name1=val1
     >CLIENT:ENV,name2=val2
     >CLIENT:ENV,...
     >CLIENT:ENV,END
 
 (3) Notify existing client disconnection.  The environmental variables passed

     are equivalent to those that would be passed to a --client-disconnect
     script.
 
     >CLIENT:DISCONNECT,{CID}
     >CLIENT:ENV,name1=val1
     >CLIENT:ENV,name2=val2
     >CLIENT:ENV,...
     >CLIENT:ENV,END
 

 (4) Notify that a particular virtual address or subnet

     is now associated with a specific client.
 
     >CLIENT:ADDRESS,{CID},{ADDR},{PRI}
 
 Variables:
 
 CID --  Client ID, numerical ID for each connecting client, sequence = 0,1,2,...
 KID --  Key ID, numerical ID for the key associated with a given client TLS session,
         sequence = 0,1,2,...
 PRI --  Primary (1) or Secondary (0) VPN address/subnet.  All clients have at least
         one primary IP address.  Secondary address/subnets are associated with
         client-specific "iroute" directives.
 ADDR -- IPv4 address/subnet in the form 1.2.3.4 or 1.2.3.0/255.255.255.0
 
 In the unlikely scenario of an extremely long-running OpenVPN server,
 CID and KID should be assumed to recycle to 0 after (2^32)-1, however this
 recycling behavior is guaranteed to be collision-free.
 

 Command Parsing
 ---------------
 

 The management interface uses the same command line lexical analyzer
 as is used by the OpenVPN config file parser.

 
 Whitespace is a parameter separator.
 

 Double quotation or single quotation characters ("", '') can be used
 to enclose parameters containing whitespace.

 
 Backslash-based shell escaping is performed, using the following

 mappings, when not in single quotations:

 
 \\       Maps to a single backslash character (\).
 \"       Pass a literal doublequote character ("), don't
          interpret it as enclosing a parameter.
 \[SPACE] Pass a literal space or tab character, don't
          interpret it as a parameter delimiter.

 
 Challenge/Response Protocol
 ---------------------------
 
 The OpenVPN Challenge/Response Protocol allows an OpenVPN server to
 generate challenge questions that are shown to the user, and to see
 the user's responses to those challenges.  Based on the responses, the
 server can allow or deny access.
 
 In this way, the OpenVPN Challenge/Response Protocol can be used
 to implement multi-factor authentication.  Two different
 variations on the challenge/response protocol are supported: the
 "Dynamic" and "Static" protocols.
 
 The basic idea of Challenge/Response is that the user must enter an
 additional piece of information, in addition to the username and
 password, to successfully authenticate.  Normally, this information
 is used to prove that the user posesses a certain key-like device
 such as cryptographic token or a particular mobile phone.
 
 Dynamic protocol:
 
 The OpenVPN dynamic challenge/response protocol works by returning
 a specially formatted error message after initial successful
 authentication.  This error message contains the challenge question,
 and is formatted as such:
 
   CRV1:<flags>:<state_id>:<username_base64>:<challenge_text>
 
 flags: a series of optional, comma-separated flags:
  E : echo the response when the user types it
  R : a response is required
 
 state_id: an opaque string that should be returned to the server
  along with the response.
 
 username_base64 : the username formatted as base64
 
 challenge_text : the challenge text to be shown to the user
 
 Example challenge:
 
   CRV1:R,E:Om01u7Fh4LrGBS7uh0SWmzwabUiGiW6l:Y3Ix:Please enter token PIN
 
 After showing the challenge_text and getting a response from the user
 (if R flag is specified), the client should submit the following
 auth creds back to the OpenVPN server:
 
 Username: [username decoded from username_base64]
 Password: CRV1::<state_id>::<response_text>
 
 Where state_id is taken from the challenge request and response_text
 is what the user entered in response to the challenge_text.
 If the R flag is not present, response_text may be the empty
 string.
 
 Example response (suppose the user enters "8675309" for the token PIN):
 
   Username: cr1 ("Y3Ix" base64 decoded)
   Password: CRV1::Om01u7Fh4LrGBS7uh0SWmzwabUiGiW6l::8675309
 
 Static protocol:
 
 The static protocol differs from the dynamic protocol in that the
 challenge question and response field is given to the user in the
 initial username/password dialog, and the username, password, and
 response are delivered back to the server in a single transaction.
 
 The "static-challenge" directive is used to give the challenge text
 to OpenVPN and indicate whether or not the response should be echoed.
 
 When the "static-challenge" directive is used, the management
 interface will respond as such when credentials are needed:
 
   >PASSWORD:Need 'Auth' username/password SC:<ECHO>,<TEXT>
 
   ECHO: "1" if response should be echoed, "0" to not echo
   TEXT: challenge text that should be shown to the user to
       facilitate their response
 
 For example:
 
   >PASSWORD:Need 'Auth' username/password SC:1,Please enter token PIN
 
 The above notification indicates that OpenVPN needs a --auth-user-pass
 password plus a response to a static challenge ("Please enter token PIN").
 The "1" after the "SC:" indicates that the response should be echoed.
 
 The management interface client in this case should add the static
 challenge text to the auth dialog followed by a field for the user to
 enter a response.  Then the client should pack the password and response
 together into an encoded password:
 
   username "Auth" foo
   password "Auth" "SCRV1:<BASE64_PASSWORD>:<BASE64_RESPONSE>"
 
 For example, if the user entered "bar" as the password and 8675309
 as the PIN, the following management interface commands should be
 issued:
 
   username "Auth" foo
   password "Auth" "SCRV1:Zm9v:ODY3NTMwOQ=="
 
 Client-side support for challenge/response protocol:
 
 Currently, the Access Server client and standalone OpenVPN
 client support both static and dynamic challenge/response
 protocols.  However, any OpenVPN client UI that drives OpenVPN
 via the management interface needs to add explicit support
 for the challenge/response protocol.