GENERAL INFORMATION

The TURN Server project contains the source code of a TURN server and TURN client 
messaging library. Also, some extra programs provided, for testing-only 
purposes. 

See the INSTALL file for the building instructions.

After the build, you will have the following binary images:

1.	turnserver: TURN Server relay. 
The compiled binary image of the TURN Server program is located in bin/ sub-directory.

2.	turnadmin: TURN administration tool. See README.turnadmin and turnadmin man page.
  
3.	turnutils_uclient. See README.turnutils and turnutils man page.

4.	turnutils_peer. See README.turnutils and turnutils man page.
   
5.	turnutils_stunclient. See README.turnutils and turnutils man page.
  
6.	turnutils_rfc5769check. See README.turnutils and turnutils man page.

In the "examples/scripts" sub-directory, you will find the examples of command lines to be used 
to run the programs. The scripts are meant to be run from examples/ sub-directory, for example:

$ cd examples
$ ./scripts/secure_relay.sh
  
RUNNING THE TURN SERVER

Options note: turnserver has long and short option names, for most options.
Some options have only long form, some options have only short form. Their syntax 
somewhat different, if an argument is required:

The short form must be used as this (for example):

  $ turnserver -L 12.34.56.78
  
The long form equivalent must use the "=" character:

  $ turnserver --listening-ip=12.34.56.78
  
If this is a flag option (no argument required) then their usage are the same, for example:

 $ turnserver -a
 
is equivalent to:

 $ turnserver --lt-cred-mech
  
=====================================

  NAME
  
turnserver - a TURN relay server implementation.
  
  SYNOPSIS
  
$ turnserver [-n | -c <config-file> ] [flags] [ --userdb=<userdb-file> | --psql-userdb=<db-conn-string> | --mysql-userdb=<db-conn-string>  | --mongo-userdb=<db-conn-string>  | --redis-userdb=<db-conn-string> ] [-z | --no-auth | -a | --lt-cred-mech ] [options]
$ turnserver -h
  
  DESCRIPTION						
  
Config file settings:  

-n		Do not use configuration file, use only command line parameters.

-c		Configuration file name (default - turnserver.conf).
		The format of config file can be seen in
		the supplied examples/etc/turnserver.conf example file. Long 
		names of the options are used as the configuration 
		items names in the file. If not an absolute path is supplied, 
		then the file is searched in the following directories: 
		  * current directory
		  * current directory etc/ sub-directory
		  * upper directory level etc/
		  * /etc/ 
		  * /usr/local/etc/
		  * installation directory /etc

User database settings:  

-b, --db, --userdb	SQLite user database file name (default - /var/db/turndb or
		/usr/local/var/db/turndb or /var/lib/turn/turndb).
				  
-e, --psql-userdb	User database connection string for PostgreSQL.
		This database can be used for long-term credentials mechanism,
		and it can store the secret value 
		for secret-based timed authentication in TURN REST API.
		The connection string format is like that:
		 
		"host=<host> dbname=<dbname> user=<db-user> password=<db-user-password> connect_timeout=<seconds>" 
		(for 8.x or newer Postgres).
		
		Or:
		
		"postgresql://username:password@hostname:port/databasename" 
		(for 9.x or newer Postgres). 

		See the INSTALL file for more explanations and examples.
		
		Also, see http://www.PostgreSQL.org for full PostgreSQL documentation.
				  
-M, --mysql-userdb	User database connection string for MySQL or MariaDB. 
		This database can be used for long-term credentials mechanism,
		and it can store the secret value for 
		secret-based timed authentication in TURN REST API.
		The connection string format is like that:
		 
		"host=<host> dbname=<dbname> user=<db-user> password=<db-user-password> connect_timeout=<seconds> read_timeout=<seconds>"

		See the INSTALL file for more explanations and examples.
		
		Also, see http://www.mysql.org or http://mariadb.org 
		for full MySQL documentation.
		
		Optional connection string parameters for the secure communications (SSL): 
		ca, capath, cert, key, cipher 
		(see http://dev.mysql.com/doc/refman/5.1/en/ssl-options.html for the 
		command options description).
		
--secret-key-file 	This is the file path which contain secret key of aes encryption while using MySQL password encryption.
			If you want to use in the MySQL connection string the password in encrypted format,
			then set in this option the file path of the secret key. The key which is used to encrypt MySQL password.
			Warning: If this option is set, then MySQL password must be set in "mysql-userdb" option in encrypted format! 
			If you want to use cleartext password then do not set this option!
-J, --mongo-userdb	User database connection string for MongoDB. 
		This database can be used for long-term credentials mechanism,
		and it can store the secret value 
		for secret-based timed authentication in TURN REST API.
		The connection string format is like that:
		 
		"mongodb://username:password@host:port/database?options"

		See the INSTALL file for more explanations and examples.
		
		Also, see http://docs.mongodb.org/manual/
		for full MongoDB documentation.
		
-N, --redis-userdb	User database connection string for Redis. 
		This database can be used for long-term	credentials mechanism,
		and it can store the secret 
		value for secret-based timed authentication in TURN REST API.
		The connection string format is like that:
		 
		"ip=<ip-addr> dbname=<db-number> password=<db-password> connect_timeout=<seconds>"

		See the INSTALL file for more explanations and examples.
		
		Also, see http://redis.io for full Redis documentation.

Flags:   

-v, --verbose		Moderate verbose mode.

-V, --Verbose		Extra verbose mode, very annoying and not recommended.

-o, --daemon		Run server as daemon.

--prod       	 	Production mode: hide the software version.

-f, --fingerprint	Use fingerprints in the TURN messages. If an incoming request
			contains a fingerprint, then TURN server will always add 
			fingerprints to the messages in this session, regardless of the
			per-server setting.

-a, --lt-cred-mech	Use long-term credentials mechanism (this one you need for WebRTC usage).

-z, --no-auth		Do not use any credentials mechanism, allow anonymous access. 
			Opposite to -a and -A options. This is default option when no 
			authentication-related options are set.
			By default, no credential mechanism is used -
			any user is allowed.

--use-auth-secret	TURN REST API flag.
			Flag that sets a special WebRTC authorization option 
			that is based upon authentication secret. The feature purpose 
			is to support "TURN Server REST API" as described in
			the TURN REST API section below.
			This option uses timestamp as part of combined username:
			usercombo -> "timestamp:username",
			turn user -> usercombo,
			turn password -> base64(hmac(input_buffer = usercombo, key = shared-secret)).
			This allows TURN credentials to be accounted for a specific user id.
			If you don't have a suitable id, the timestamp alone can be used.
			This option is just turns on secret-based authentication.
			The actual value of the secret is defined either by option static-auth-secret,
			or can be found in the turn_secret table in the database.
			
--oauth			Support oAuth authentication, as in the third-party STUN/TURN RFC 7635.
			
--dh566			Use 566 bits predefined DH TLS key. Default size of the key is 1066.

--dh2066		Use 2066 bits predefined DH TLS key. Default size of the key is 1066.

--no-tlsv1		Do not allow TLSv1/DTLSv1 protocol.

--no-tlsv1_1		Do not allow TLSv1.1 protocol.

--no-tlsv1_2		Do not allow TLSv1.2/DTLSv1.2 protocol.

--no-udp		Do not start UDP client listeners.

--no-tcp		Do not start TCP client listeners.

--no-tls		Do not start TLS client listeners.

--no-dtls		Do not start DTLS client listeners.

--no-udp-relay		Do not allow UDP relay endpoints defined in RFC 5766, 
			use only TCP relay endpoints as defined in RFC 6062.

--no-tcp-relay		Do not allow TCP relay endpoints defined in RFC 6062, 
			use only UDP relay endpoints as defined in RFC 5766. 

--no-stdout-log		Flag to prevent stdout log messages.
			By default, all log messages are going to both stdout and to
			the configured log file. With this option everything will be going to 
			the log file only (unless the log file itself is stdout).
			
--syslog		With this flag, all log will be redirected to the system log (syslog).

--simple-log		This flag means that no log file rollover will be used, and the log file
			name will be constructed as-is, without PID and date appendage.
			This option can be used, for example, together with the logrotate tool.
				
--secure-stun		Require authentication of the STUN Binding request.
			By default, the clients are allowed anonymous access to the STUN Binding functionality.

-S, --stun-only		Run as STUN server only, all TURN requests will be ignored. 
			Option to suppress TURN functionality, only STUN requests will be processed.

--no-stun		Run as TURN server only, all STUN requests will be ignored. 
			Option to suppress STUN functionality, only TURN requests will be processed.

--allow-loopback-peers	Allow peers on the loopback addresses (127.x.x.x and ::1).
             Allow it only for testing in a development environment! 
             In production it adds a possible security vulnerability, 
             and so due to security reasons, it is not allowed 
             using it together with empty cli-password.

--no-multicast-peers	Disallow peers on well-known broadcast addresses 
			(224.0.0.0 and above, and FFXX:*).

--mobility		Mobility with ICE (MICE) specs support.

--no-cli		Turn OFF the CLI support. By default it is always ON.
			See also options --cli-ip and --cli-port.
				
--server-relay		Server relay. NON-STANDARD AND DANGEROUS OPTION. 
			Only for those applications when we want to run 
			server applications on the relay endpoints.
			This option eliminates the IP permissions check 
			on the packets incoming to the relay endpoints.
			See http://tools.ietf.org/search/rfc5766#section-17.2.3 .
				
--udp-self-balance	(recommended for older Linuxes only)
			Automatically balance UDP traffic over auxiliary servers
			(if configured). The load balancing is using the 
			ALTERNATE-SERVER mechanism. The TURN client must support 
			300 ALTERNATE-SERVER response for this functionality.
			
--check-origin-consistency	The flag that sets the origin consistency 
			check: across the session, all requests must have the same
			main ORIGIN attribute value (if the ORIGIN was
			initially used by the session).

-h			Help.
    
Options with values:  

--stale-nonce[=<value>]		Use extra security with nonce value having
							limited lifetime, in seconds (default 600 secs).

--max-allocate-lifetime		Set the maximum value for the allocation lifetime.
							Default to 3600 secs.

--channel-lifetime 	Set the lifetime for channel binding, default to 600 secs.
					This value MUST not be changed for production purposes.

--permission-lifetime	Set the value for the lifetime of the permission.
					Default to 300 secs.
					This MUST not be changed for production purposes.

-d, --listening-device	Listener interface device.
			(NOT RECOMMENDED. Optional functionality, Linux only). 
			The turnserver process must have root privileges to bind the 
			listening endpoint to a device. If turnserver must run as a 
			process without root privileges, then just do not use this setting.

-L, --listening-ip	Listener IP address of relay server. 
			Multiple listeners can be specified, for example:
			-L ip1 -L ip2 -L ip3
			If no IP(s) specified, then all IPv4 and 
			IPv6 system IPs will be used for listening.
			The same ip(s) can be used as both listening and relay ip(s).

-p, --listening-port	TURN listener port for UDP and TCP listeners (Default: 3478).
			Note: actually, TLS & DTLS sessions can connect to the "plain" TCP & UDP
			port(s), too - if allowed by configuration.

--tls-listening-port	TURN listener port for TLS and DTLS listeners (Default: 5349).
			Note: actually, "plain" TCP & UDP sessions can connect to the TLS & DTLS
			port(s), too - if allowed by configuration. The TURN server 
			"automatically" recognizes the type of traffic. Actually, two listening
			endpoints (the "plain" one and the "tls" one) are equivalent in terms of
			functionality; but we keep both endpoints to satisfy the RFC 5766 specs.
			For secure TCP connections, we currently support SSL version 3 and 
			TLS versions 1.0, 1.1, 1.2.
			For secure UDP connections, we support DTLS version 1.

--alt-listening-port	Alternative listening port for UDP and TCP listeners;
			default (or zero) value means "listening port plus one".
			This is needed for STUN CHANGE_REQUEST - in RFC 5780 sense
                	or in old RFC 3489 sense - for NAT behavior discovery). The TURN Server
			supports CHANGE_REQUEST only if it is started with more than one
			listening IP address of the same family (IPv4 or IPv6). The CHANGE_REQUEST
			is only supported by UDP protocol, other protocols are listening
			on that endpoint only for "symmetry".

--alt-tls-listening-port	Alternative listening port for TLS and DTLS protocols.
			Default (or zero) value means "TLS listening port plus one".
				
--aux-server		Auxiliary STUN/TURN server listening endpoint.
			Aux servers have almost full TURN and STUN functionality.
			The (minor) limitations are:
				1) Auxiliary servers do not have alternative ports and
				they do not support STUN RFC 5780 functionality (CHANGE REQUEST).
				2) Auxiliary servers also are never returning ALTERNATIVE-SERVER reply.
					
			Valid formats are 1.2.3.4:5555 for IPv4 and [1:2::3:4]:5555 for IPv6.
			There may be multiple aux-server options, each will be used for listening
			to client requests.

-i, --relay-device	Relay interface device for relay sockets 
			(NOT RECOMMENDED. Optional, Linux only).

-E, --relay-ip		Relay address (the local IP address that 
			will be used to relay the packets to the 
			peer). Multiple relay addresses may be used:
			-E ip1 -E ip2 -E ip3
			The same IP(s) can be used as both listening IP(s) and relay IP(s).
			If no relay IP(s) specified, then the turnserver will apply the 
			default policy: it will decide itself which relay addresses to be 
			used, and it will always be using the client socket IP address as 
			the relay IP address of the TURN session (if the requested relay 
			address family is the same as the family of the client socket).

-X, --external-ip	TURN Server public/private address mapping, if the server is behind NAT.
			In that situation, if a -X is used in form "-X <ip>" then that ip will be reported
			as relay IP address of all allocations. This scenario works only in a simple case
			when one single relay address is be used, and no CHANGE_REQUEST functionality is 
			required. That single relay address must be mapped by NAT to the 'external' IP.
			The "external-ip" value, if not empty, is returned in XOR-RELAYED-ADDRESS field.
			For that 'external' IP, NAT must forward ports directly (relayed port 12345
			must be always mapped to the same 'external' port 12345).
			In more complex case when more than one IP address is involved,
			that option must be used several times, each entry must
			have form "-X <public-ip/private-ip>", to map all involved addresses.
			CHANGE_REQUEST (RFC5780 or RFC3489) NAT discovery STUN functionality will work 
			correctly, if the addresses are mapped properly, even when the TURN server itself 
			is behind A NAT.
			By default, this value is empty, and no address mapping is used.
				
-m, --relay-threads	Number of the relay threads to handle the established connections
			(in addition to authentication thread and the listener thread).
			If explicitly set to 0 then application runs relay process in a single thread,
			in the same thread with the listener process (the authentication thread will 
			still be a separate thread). If not set, then a default optimal algorithm 
			will be employed (OS-dependent). In the older Linux systems
			(before Linux kernel 3.9), the number of UDP threads is always one threads 
			per network listening endpoint - unless "-m 0" or "-m 1" is set.

--min-port		Lower bound of the UDP port range for relay 
			endpoints allocation.
			Default value is 49152, according to RFC 5766.

--max-port		Upper bound of the UDP port range for relay 
			endpoints allocation.
			Default value is 65535, according to RFC 5766.

-u, --user		Long-term security mechanism credentials user account, 
			in the column-separated form username:key. 
			Multiple user accounts may be used in the command line.
			The key is either the user password, or
			the key is generated
			by turnadmin command. In the second case,
			the key must be prepended with 0x symbols.
			The key is calculated over the user name, 
			the user realm, and the user password.
			This setting may not be used with TURN REST API.

-r, --realm		The default realm to be used for the users when no explicit 
			origin/realm relationship was found in the database, or if the TURN
			server is not using any database (just the commands-line settings
			and the userdb file). Must be used with long-term credentials 
			mechanism or with TURN REST API.

-C, --rest-api-separator	This is the timestamp/username separator symbol 
			(character) in TURN REST API. The default value is :.

-q, --user-quota	Per-user allocations quota: how many concurrent 
			allocations a user can create. This option can also be set 
			through the database, for a particular realm.

-Q, --total-quota	Total allocations quota: global limit on concurrent allocations.
			This option can also be set through the database, for a particular realm.

-s, --max-bps		Max bytes-per-second bandwidth a TURN session is allowed to handle
			(input and output network streams are treated separately). Anything above 
			that limit will be dropped or temporary suppressed (within the
			available buffer limits). This option can also be set through the 
			database, for a particular realm.
			
-B, --bps-capacity	Maximum server capacity.
			Total bytes-per-second bandwidth the TURN server is allowed to allocate
			for the sessions, combined (input and output network streams are treated
			separately).

--static-auth-secret	Static authentication secret value (a string) for TURN REST API only.
			If not set, then the turn server will try to use the dynamic value 
			in turn_secret table in user database (if present). The database-stored
			value can be changed on-the-fly by a separate program, so this is why
			that other mode is dynamic. Multiple shared secrets can be used
			(both in the database and in the "static" fashion).
			
--server-name		Server name used for
			the oAuth authentication purposes.
			The default value is the realm name.

--cert			Certificate file, PEM format. Same file 
			search rules applied as for the configuration 
			file. If both --no-tls and --no-dtls options 
			are specified, then this parameter is not needed.
			Default value is turn_server_cert.pem.

--pkey		     	Private key file, PEM format. Same file 
			search rules applied as for the configuration 
			file. If both --no-tls and --no-dtls options 
			are specified, then this parameter is not needed.
			Default value is turn_server_pkey.pem.
			
--pkey-pwd		If the private key file is encrypted, then this password to be used.

--cipher-list		Allowed OpenSSL cipher list for TLS/DTLS connections.
			Default value is "DEFAULT".
				
--CA-file		CA file in OpenSSL format. 
			Forces TURN server to verify the client SSL certificates.
			By default, no CA is set and no client certificate check is performed.

--ec-curve-name		Curve name for EC ciphers, if supported by OpenSSL 
			library (TLS and DTLS). The default value is prime256v1, 
			if pre-OpenSSL 1.0.2 is used. With OpenSSL 1.0.2+,
			an optimal curve will be automatically calculated, if not defined
			by this option.

--dh-file		Use custom DH TLS key, stored in PEM format in the file.
			Flags --dh566 and --dh2066 are ignored when the DH key is taken from a file.

-l, --log-file		Option to set the full path name of the log file.
			By default, the turnserver tries to open a log file in 
			/var/log/turnserver, /var/log, /var/tmp, /tmp and . (current) 
			directories (which file open operation succeeds 
			first that file will be used). With this option you can set the 
			definite log file name.
			The special names are "stdout" and "-" - they will force everything 
			to the stdout. Also, "syslog" name will redirect everything into
			the system log (syslog), as if the option "--syslog" was set. 
			In the runtime, the logfile can be reset with the SIGHUP signal 
			to the turnserver process.
				
--alternate-server	Option to set the "redirection" mode. The value of this option
			will be the address of the alternate server for UDP & TCP service in form of 
			<ip>[:<port>]. The server will send this value in the attribute
			ALTERNATE-SERVER, with error 300, on ALLOCATE request, to the client.
			Client will receive only values with the same address family
			as the client network endpoint address family. 
			See RFC 5389 and RFC 5766 for ALTERNATE-SERVER functionality description. 
			The client must use the obtained value for subsequent TURN communications.
			If more than one --alternate-server options are provided, then the functionality
			can be more accurately described as "load-balancing" than a mere "redirection". 
			If the port number is omitted, then the default port 
			number 3478 for the UDP/TCP protocols will be used.
			Colon (:) characters in IPv6 addresses may conflict with the syntax of 
			the option. To alleviate this conflict, literal IPv6 addresses are enclosed 
			in square brackets in such resource identifiers, for example: 
			[2001:db8:85a3:8d3:1319:8a2e:370:7348]:3478 . 
			Multiple alternate servers can be set. They will be used in the
			round-robin manner. All servers in the pool are considered of equal weight and 
			the load will be distributed equally. For example, if we have 4 alternate servers, 
			then each server will receive 25% of ALLOCATE requests. An alternate TURN server 
			address can be used more than one time with the alternate-server option, so this 
			can emulate "weighting" of the servers. 

--tls-alternate-server	Option to set alternative server for TLS & DTLS services in form of 
			<ip>:<port>. If the port number is omitted, then the default port 
			number 5349 for the TLS/DTLS protocols will be used. See the 
			previous option for the functionality description.

-O, --redis-statsdb	Redis status and statistics database connection string, if used (default - empty, 
			no Redis stats DB used). This database keeps allocations status information, and it can 
			be also used for publishing and delivering traffic and allocation event notifications.
			This database option can be used independently of --redis-userdb option,
			and actually Redis can be used for status/statistics and SQLite or MySQL or MongoDB or 
			PostgreSQL can be used for the user database.
			The connection string has the same parameters as redis-userdb connection string.

--max-allocate-timeout	Max time, in seconds, allowed for full allocation establishment. 
			Default is 60 seconds.

--denied-peer-ip=<IPaddr[-IPaddr]>

--allowed-peer-ip=<IPaddr[-IPaddr]> Options to ban or allow specific ip addresses or ranges 
			of ip addresses. If an ip address is specified as both allowed and denied, then 
			the ip address is considered to be allowed. This is useful when you wish to ban
			a range of ip addresses, except for a few specific ips within that range.
			This can be used when you do not want users of the turn server to be able to access
			machines reachable by the turn server, but would otherwise be unreachable from the 
			internet (e.g. when the turn server is sitting behind a NAT). The 'white" and "black" peer 
			IP ranges can also be dynamically changed in the database. 
			The allowed/denied addresses (white/black lists) rules are very simple:
			1) If there is no rule for an address, then it is allowed; 
			2) If there is an "allowed" rule that fits the address then it is allowed - no matter what;
			3) If there is no "allowed" rule that fits the address, and if there is a "denied" rule that
			fits the address, then it is denied.

--pidfile 		File name to store the pid of the process.
			Default is /var/run/turnserver.pid (if superuser account is used) or
			/var/tmp/turnserver.pid .
				
--proc-user		User name to run the process. After the initialization, the turnserver process
			will make an attempt to change the current user ID to that user.
	
--proc-group		Group name to run the process. After the initialization, the turnserver process
			will make an attempt to change the current group ID to that group.

-K, --keep-address-family		TURN server allocates address family according TURN
			Client <=> Server communication address family.
			!! It breaks RFC6156 section-4.2 (violates default IPv4) !!

--cli-ip		Local system IP address to be used for CLI management interface.
			The turnserver process can be accessed for management with telnet,
			at this IP address and on the CLI port (see the next parameter). 
			Default value is 127.0.0.1. You can use telnet or putty (in telnet mode)
			to access the CLI management interface. 
					
--cli-port		CLI management interface listening port. Default is 5766.

--cli-password		CLI access password. Default is empty (no password).
			For the security reasons, it is recommended to use the encrypted
			form of the password (see the -P command in the turnadmin
			utility). The dollar signs in the encrypted form must be escaped.

--cli-max-output-sessions	Maximum number of output sessions in ps CLI command.
			This value can be changed on-the-fly in CLI. The default value is 256.

--web-admin		Enable Turn Web-admin support. By default it is disabled.

--web-admin-ip=<IP>	Local system IP address to be used for Web-admin server endpoint. Default value is 127.0.0.1.

--web-admin-port=<port>  Web-admin server port. Default is 8080.
--web-admin-listen-on-workers   Enable for web-admin server to listens on STUN/TURN workers STUN/TURN ports.
			By default it is disabled for security resons!
			(This behavior used to be the default behavior, and was enabled by default.)

--ne=[1|2|3]		Set network engine type for the process (for internal purposes).

==================================

LOAD BALANCE AND PERFORMANCE TUNING

This topic is covered in the wiki page:

https://github.com/coturn/coturn/wiki/turn_performance_and_load_balance
	 
===================================

WEBRTC USAGE

This is a set of notes for the WebRTC users:

1) WebRTC uses long-term authentication mechanism, so you have to use -a 
option (or --lt-cred-mech). WebRTC relaying will not work with anonymous
access. With -a option, do not forget to set the 
default realm (-r option). You will also have to set up the user accounts, 
for that you have a number of options:

	a) command-line options (-u).
	
	b) a database table (SQLite or PostgreSQL or MySQL or MongoDB). You will have to 
	set keys with turnadmin utility (see docs and wiki for turnadmin). 
	You cannot use open passwords in the database.

	c) Redis key/value pair(s), if Redis is used. You key use either keys or 
	open passwords with Redis; see turndb/testredisdbsetup.sh file.  
	
	d) You also can use the TURN REST API. You will need shared secret(s) set
	either	through the command line option, or through the config file, or through
	the database table or Redis key/value pairs.  

2) Usually WebRTC uses fingerprinting (-f).

3) -v option may be nice to see the connected clients.

4) -X is needed if you are running your TURN server behind a NAT.

5) --min-port and --max-port may be needed if you want to limit the relay endpoints ports 
number range.

===================================

TURN REST API

In WebRTC, the browser obtains the TURN connection information from the web
server. This information is a secure information - because it contains the 
necessary TURN credentials. As these credentials are transmitted over the 
public networks, we have a potential security breach.

If we have to transmit a valuable information over the public network, 
then this information has to have a limited lifetime. Then the guy who 
obtains this information without permission will be able to perform 
only limited damage.

This is how the idea of TURN REST API - time-limited TURN credentials - 
appeared. This security mechanism is based upon the long-term credentials 
mechanism. The main idea of the REST API is that the web server provides 
the credentials to the client, but those credentials can be used only 
limited time by an application that has to create a TURN server connection.

The "classic" long-term credentials mechanism (LTCM) is described here:

http://tools.ietf.org/html/rfc5389#section-10.2

http://tools.ietf.org/html/rfc5389#section-15.4

For authentication, each user must know two things: the username and the
password. Optionally, the user must supply the ORIGIN value, so that the
server can figure out the realm to be used for the user. The nonce and 
the realm values are supplied by the TURN server. But LTCM is not saying 
anything about the nature and about the persistence of the username and 
of the password; and this is used by the REST API.

In the TURN REST API, there is no persistent passwords for users. A user has 
just the username. The password is always temporary, and it is generated by 
the web server on-demand, when the user accesses the WebRTC page. And, 
actually, a temporary one-time session only, username is provided to the user, 
too. 

The temporary user is generated as:

temporary-username="timestamp" + ":" + "username"

where username is the persistent user name, and the timestamp format is just 
seconds since 1970 - the same value as time(NULL) function returns.

The temporary password is obtained as HMAC-SHA1 function over the temporary
username, with shared secret as the HMAC key, and then the result is encoded:

temporary-password = base64_encode(hmac-sha1(shared-secret, temporary-username))

Both the TURN server and the web server know the same shared secret. How the
shared secret is distributed among the involved entities is left to the WebRTC
deployment details - this is beyond the scope of the TURN REST API.

So, a timestamp is used for the temporary password calculation, and this 
timestamp can be retrieved from the temporary username. This information
is valuable, but only temporary, while the timestamp is not expired. Without
knowledge of the shared secret, a new temporary password cannot be generated.

This is all formally described in Justin's Uberti TURN REST API document
that can be obtained following the link "TURN REST API" in the TURN Server
project's page https://github.com/coturn/coturn/.

Once the temporary username and password are obtained by the client (browser)
application, then the rest is just 'classic" long-term credentials mechanism.
For developers, we are going to describe it step-by-step below:

  - a new TURN client sends a request command to the TURN server. Optionally, 
  it adds the ORIGIN field to it. 
  - TURN server sees that this is a new client and the message is not 
  	authenticated.
  - the TURN server generates a random nonce string, and return the 
  	error 401 to the client, with nonce and realm included. If the ORIGIN
  	field was present in the client request, it may affect the realm value
  	that the server chooses for the client.
  - the client sees the 401 error and it extracts two values from 
  	the error response: the nonce and the realm.
  - the client uses username, realm and password to produce a key:

         key = MD5(username ":" realm ":" SASLprep(password))
 (SASLprep is described here: http://tools.ietf.org/html/rfc4013)
 
  - the client forms a new request, adds username, realm and nonce to the 
  	request. Then, the client calculates and adds the integrity field to 
  	the request. This is the trickiest part of the process, and it is
  	 described in the end of section 15.4: 
  	http://tools.ietf.org/html/rfc5389#section-15.4
  - the client, optionally, adds the fingerprint field. This may be also 
  	a tricky procedure, described in section 15.5 of the same document. 
  	WebRTC usually uses fingerprinted TURN messages.
  - the TURN server receives the request, reads the username.
  - then the TURN server checks that the nonce and the realm in the request 
  	are the valid ones.
  - then the TURN server calculates the key.
  - then the TURN server calculates the integrity field.
  - then the TURN server compares the calculated integrity field with the 
  	received one - they must be the same. If the integrity fields differ, 
  	then the request is rejected.

In subsequent communications, the client may go with exactly the same 
sequence, but for optimization usually the client, having already 
information about realm and nonce, pre-calculates the integrity string 
for each request, so that the 401 error response becomes unnecessary. 
The TURN server may use "--stale-nonce" option for extra security: in 
some time, the nonce expires and the client will obtain 438 error response
with the new nonce, and the client will have to start using the new nonce.

In subsequent communications, the server and the client will always assume 
the same password - the original password becomes the session parameter and 
is never expiring. So the password is not changing while the session is valid
and unexpired. So, if the session is properly maintained, it may go forever, 
even if the user password has been already changed (in the database). The 
session simply is using the old password. Once the session got disconnected, 
the client will have to use the new password to re-connect (if the password 
has been changed).

An example when a new shared secret is generated every hour by the TURN server
box and then supplied to the web server, remotely, is provided in the script
examples/scripts/restapi/shared_secret_maintainer.pl .

A very important thing is that the nonce must be totally random and it must be 
different for different clients and different sessions. 
	 
===================================

DATABASES

For the user database, the turnserver has the following options:

1) Users can be set in the command line, with multiple -u or --user options. 
Obviously, only a few users can be set that way, and their credentials are fixed 
for the turnserver process lifetime.

2) Users can be stored in SQLite DB. The default SQLite database file is /var/db/turndb
or /usr/local/var/db/turndb or /var/lib/turn/turndb.

3) Users can be stored in PostgreSQL database, if the turnserver was compiled with PostgreSQL
support. Each time turnserver checks user credentials, it reads the database (asynchronously,
of course, so that the current flow of packets is not delayed in any way), so any change in the 
database content is immediately visible by the turnserver. This is the way if you need the 
best scalability. The schema for the database can be found in schema.sql file.
For long-term credentials, you have to set the "keys" for the users; the "keys" are generated 
by the turnadmin utility. For the key generation, you need username, password and the realm. 
All users in the database must use the same realm value; if down the road you will decide 
to change the realm name, then you will have to re-generate all user keys (that can be done 
in a batch script). See the file turndb/testsqldbsetup.sql as an example.

4) The same is true for MySQL database. The same schema file is applicable. 
The same considerations are applicable. 

5) The same is true for the Redis database, but the Redis database has aa different schema -
it can be found (in the form of explanation) in schema.userdb.redis. 
Also, in Redis you can store both "keys" and open passwords (for long term credentials) - 
the "open password" option is less secure but more convenient for low-security environments. 
See the file turndb/testredisdbsetup.sh as an example. 

6) If a database is used, then users can be divided into multiple independent realms. Each realm
can be administered separately, and each realm can have its own set of users and its own
performance options (max-bps, user-quota, total-quota).

7) If you use MongoDB, the database will be setup for you automatically.

8) Of course, the turnserver can be used in non-secure mode, when users are allowed to establish
sessions anonymously. But in most cases (like WebRTC) that will not work.

For the status and statistics database, there are two choices:

1) The simplest choice is not to use it. Do not set --redis-statsdb option, and this functionality 
will be simply ignored.

2) If you choose to use it, then set the --redis-statsdb option. This may be the same database
as in --redis-userdb option, or it may be a different database. You may want to use different 
database for security or convenience reasons. Also, you can use different database management
systems for the user database and for the ststus and statistics database. For example, you can use 
MySQL as the user database, and you can use redis for the statistics. Or you can use Redis for both.

So, we have 6 choices for the user management, and 2 choices for the statistics management. These
two are totally independent. So, you have overall 6*2=12 ways to handle persistent information, 
choose any for your convenience.

You do not have to handle the database information "manually" - the turnadmin program can handle 
everything for you. For PostgreSQL and MySQL you will just have to create an empty database
with schema.sql SQL script. With Redis, you do not have to do even that - just run turnadmin and 
it will set the users for you (see the turnadmin manuals). If you are using SQLite, then the 
turnserver or turnadmin will initialize the empty database, for you, when started. The 
TURN server installation process creates an empty initialized SQLite database in the default 
location (/var/db/turndb or /usr/local/var/db/turndb or /var/lib/turn/turndb, depending on the system).

=================================

ALPN

The server supports ALPNs "stun.turn" and "stun.nat-discovery", when
compiled with OpenSSL 1.0.2 or newer. If the server receives a TLS/DTLS
ClientHello message that contains one or both of those ALPNs, then the
server chooses the first stun.* label and sends it back (in the ServerHello)
in the ALPN extension field. If no stun.* label is found, then the server
does not include the ALPN information into the ServerHello.

=================================

LIBRARIES

In the lib/ sub-directory the build process will create TURN client messaging library.
In the include/ sub-directory, the necessary include files will be placed.
The C++ wrapper for the messaging functionality is located in TurnMsgLib.h header.
An example of C++ code can be found in stunclient.c file. 

=================================

DOCS

After installation, run the command:

$ man turnserver

or in the project root directory:

$ man -M man turnserver

to see the man page.

In the docs/html subdirectory of the original archive tree, you will find the client library 
reference. After the installation, it will be placed in PREFIX/share/doc/turnserver/html.

=================================

LOGS

When the TURN Server starts, it makes efforts to create a log file turn_<pid>.log 
in the following directories:

	* /var/log
	* /log/
	* /var/tmp
	* /tmp
	* current directory

If all efforts failed (due to the system permission settings) then all 
log messages are sent only to the standard output of the process.

This behavior can be controlled by --log-file, --syslog and --no-stdout-log
options.

=================================

HTTPS MANAGEMENT INTERFACE

The turnserver process provides an HTTPS Web access as statistics and basic
management interface. The turnserver listens to incoming HTTPS admin 
connections on the same ports as the main TURN/STUN listener. The Web admin
pages are basic and self-explanatory.

To make the HTTPS interface active, the database table admin_user must be
populated with the admin user account(s). An admin user can be a superuser
(if not assigned to a particular realm) or a restricted user (if assigned to
a realm). The restricted admin users can perform only limited actions, within
their corresponding realms.

=================================

TELNET CLI

The turnserver process provides a telnet CLI access as statistics and basic management
interface. By default, the turnserver starts a telnet CLI listener on IP 127.0.0.1 and
port 5766. That can be changed by the command-cline options of the turnserver process
(see --cli-ip and --cli-port options). The full list of telnet CLI commands is provided
in "help" command output in the telnet CLI.

=================================

CLUSTERS

TURN Server can be a part of the cluster installation. But, to support the "even port" functionality 
(RTP/RTCP streams pairs) the client requests from a particular IP must be delivered to the same 
TURN Server instance, so it requires some networking setup massaging for the cluster. The reason is that 
the RTP and RTCP relaying endpoints must be allocated on the same relay IP. It would be possible 
to design a scheme with the application-level requests forwarding (and we may do that later) but 
it would affect the performance.

=================================

FILES

/etc/turnserver.conf

/var/db/turndb

/usr/local/var/db/turndb

/var/lib/turn/turndb

/usr/local/etc/turnserver.conf

=================================

DIRECTORIES

/usr/local/share/turnserver

/usr/local/share/doc/turnserver

/usr/local/share/examples/turnserver

=================================

STANDARDS

obsolete STUN RFC 3489

new STUN RFC 5389

TURN RFC 5766

TURN-TCP extension RFC 6062
 
TURN IPv6 extension RFC 6156

STUN/TURN test vectors RFC 5769

STUN NAT behavior discovery RFC 5780

=================================

SEE ALSO

	turnadmin, turnutils

======================================

  WEB RESOURCES

project page:

https://github.com/coturn/coturn/

Wiki page:

https://github.com/coturn/coturn/wiki

forum:

https://groups.google.com/forum/?fromgroups=#!forum/turn-server-project-rfc5766-turn-server

======================================

  AUTHORS

	Oleg Moskalenko <mom040267@gmail.com>

	Gabor Kovesdan http://kovesdan.org/

	Daniel Pocock http://danielpocock.com/

	John Selbie (jselbie@gmail.com)

	Lee Sylvester <lee@designrealm.co.uk>

	Erik Johnston <erikj@openmarket.com>

	Roman Lisagor <roman@demonware.net>
	
	Vladimir Tsanev <tsachev@gmail.com>
	
	Po-sheng Lin <personlin118@gmail.com>
	
	Peter Dunkley <peter.dunkley@acision.com>
	
	Mutsutoshi Yoshimoto <mutsutoshi.yoshimoto@mixi.co.jp>

	Federico Pinna <fpinna@vivocha.com>

	Bradley T. Hughes <bradleythughes@fastmail.fm>

        Mihaly Meszaros <misi@majd.eu>