Support rewriting username in MQTTS CONNECT

[dmocek]

Your Feature Request

Support rewriting username in MQTTS CONNECT to be the certificate CN or DN. See:

• How Nginx supports this
• How NetScaler supports this

What are you trying to do?

Need a way of identifying the client in MQTTS connections.

Output of haproxy -vv

HAProxy version 2.9.6-9eafce5 2024/02/26 - https://haproxy.org/
Status: stable branch - will stop receiving fixes around Q1 2025.
Known bugs: http://www.haproxy.org/bugs/bugs-2.9.6.html
Running on: Linux 5.15.0-203.146.5.1.el8uek.x86_64 #2 SMP Thu Feb 8 17:14:39 PST 2024 x86_64
Build options :
  TARGET  = linux-glibc
  CPU     = generic
  CC      = cc
  CFLAGS  = -O2 -g -Wall -Wextra -Wundef -Wdeclaration-after-statement -Wfatal-errors -Wtype-limits -Wshift-negative-value -Wshift-overflow=2 -Wduplicated-cond -Wnull-dereference -fwrapv -Wno-address-of-packed-member -Wno-unused-label -Wno-sign-compare -Wno-unused-parameter -Wno-clobbered -Wno-missing-field-initializers -Wno-cast-function-type -Wno-string-plus-int -Wno-atomic-alignment
  OPTIONS = USE_LINUX_TPROXY=1 USE_CRYPT_H=1 USE_GETADDRINFO=1 USE_OPENSSL=1 USE_LUA=1 USE_ZLIB=1 USE_NS=1 USE_SYSTEMD=1 USE_PROMEX=1 USE_PCRE=1
  DEBUG   = -DDEBUG_STRICT -DDEBUG_MEMORY_POOLS

Feature list : -51DEGREES +ACCEPT4 +BACKTRACE -CLOSEFROM +CPU_AFFINITY +CRYPT_H -DEVICEATLAS +DL -ENGINE +EPOLL -EVPORTS +GETADDRINFO -KQUEUE -LIBATOMIC +LIBCRYPT +LINUX_CAP +LINUX_SPLICE +LINUX_TPROXY +LUA +MATH -MEMORY_PROFILING +NETFILTER +NS -OBSOLETE_LINKER +OPENSSL -OPENSSL_AWSLC -OPENSSL_WOLFSSL -OT +PCRE -PCRE2 -PCRE2_JIT -PCRE_JIT +POLL +PRCTL -PROCCTL +PROMEX -PTHREAD_EMULATION -QUIC -QUIC_OPENSSL_COMPAT +RT +SHM_OPEN -SLZ +SSL -STATIC_PCRE -STATIC_PCRE2 +SYSTEMD +TFO +THREAD +THREAD_DUMP +TPROXY -WURFL +ZLIB

Default settings :
  bufsize = 16384, maxrewrite = 1024, maxpollevents = 200

Built with multi-threading support (MAX_TGROUPS=16, MAX_THREADS=256, default=2).
Built with OpenSSL version : OpenSSL 1.1.1k  FIPS 25 Mar 2021
Running on OpenSSL version : OpenSSL 1.1.1k  FIPS 25 Mar 2021
OpenSSL library supports TLS extensions : yes
OpenSSL library supports SNI : yes
OpenSSL library supports : TLSv1.0 TLSv1.1 TLSv1.2 TLSv1.3
Built with Lua version : Lua 5.4.6
Built with the Prometheus exporter as a service
Built with network namespace support.
Built with zlib version : 1.2.11
Running on zlib version : 1.2.11
Compression algorithms supported : identity("identity"), deflate("deflate"), raw-deflate("deflate"), gzip("gzip")
Built with transparent proxy support using: IP_TRANSPARENT IPV6_TRANSPARENT IP_FREEBIND
Built with PCRE version : 8.42 2018-03-20
Running on PCRE version : 8.42 2018-03-20
PCRE library supports JIT : no (USE_PCRE_JIT not set)
Encrypted password support via crypt(3): yes
Built with gcc compiler version 8.5.0 20210514 (Red Hat 8.5.0-4)

Available polling systems :
      epoll : pref=300,  test result OK
       poll : pref=200,  test result OK
     select : pref=150,  test result OK
Total: 3 (3 usable), will use epoll.

Available multiplexer protocols :
(protocols marked as <default> cannot be specified using 'proto' keyword)
         h2 : mode=HTTP  side=FE|BE  mux=H2    flags=HTX|HOL_RISK|NO_UPG
       fcgi : mode=HTTP  side=BE     mux=FCGI  flags=HTX|HOL_RISK|NO_UPG
  <default> : mode=HTTP  side=FE|BE  mux=H1    flags=HTX
         h1 : mode=HTTP  side=FE|BE  mux=H1    flags=HTX|NO_UPG
  <default> : mode=TCP   side=FE|BE  mux=PASS  flags=
       none : mode=TCP   side=FE|BE  mux=PASS  flags=NO_UPG

Available services : prometheus-exporter
Available filters :
        [BWLIM] bwlim-in
        [BWLIM] bwlim-out
        [CACHE] cache
        [COMP] compression
        [FCGI] fcgi-app
        [SPOE] spoe
        [TRACE] trace

[git001]

Looks like you would like to have something like mqtt_field_set_value similar to "GET" https://docs.haproxy.org/2.9/configuration.html#7.3.1-mqtt_field_value, right?

Maybe you can contribute that feature 😄

This are the souce links of the current feature.

haproxy/src/mqtt.c

Lines 327 to 334 in 10224d7

	/* Extracts the value of a <fieldname_id> of type <type> from a given MQTT
	* message <msg>. IST_NULL is returned if an error occurred while parsing or if
	* the field could not be found. If more data are required, the message with a
	* length set to 0 is returned. If the field is found, the response is returned
	* as a struct ist.
	*/
	struct ist mqtt_field_value(struct ist msg, int type, int fieldname_id)
	{

haproxy/src/sample.c

Lines 3953 to 3962 in 10224d7

	/*
	* Extract the field value of an input binary sample containing an MQTT packet.
	* Takes 2 mandatory arguments:
	* - packet type
	* - field name
	*
	* return 1 if the field was found, 0 if not.
	*/
	static int sample_conv_mqtt_field_value(const struct arg *arg_p, struct sample *smp, void *private)
	{