NUCLEAR-WAR created an issue (kamailio/kamailio#4291)

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### Description

Kamailio is sending wrong P-Associated-URI towards Application Server, when sending 3rd Party Registration:

Kamailio sends: ``` P-Associated-URI: <sip:0912584710@ims.mnc001.mcc001.3gppnetwork.org, tel:0912584710>, sip:001010000084710@ims.mnc001.mcc001.3gppnetwork.org

``` ABNF for the Header is (see RFC7315 Section 5.1) : ``` "P‑Associated‑URI"  HCOLON  [ p‑aso‑uri‑spec ]  *( COMMA  p‑aso‑uri‑spec )

p-aso-uri-spec = name‑addr  *( SEMI  ai‑param )

it looks like an issue in ims_isc module, as other transactions containing this header are not affected.

```

### Troubleshooting

#### Reproduction

Using any version of Kamailio in IMS Setup ( e.g like Docker_open5gs) and enable 3rd Party registration in the associated iFC of the IMS User. fur testing this particular issue any SIP Server could be user, as we need only to capture the 3rdPty Register only.

Start the registration process and capture the 3rdPty registration after a successful registration with the S-CSCF.

also, would it be possible to have multiple occurrence of this header for each IMPU, that will make it easy to use non complex logic to gather the IMPUs of a user from the AS.

#### Debugging Data

log is long, therefor I attached it to the issue along with a PCAP

#### SIP Traffic

<!-- If the issue is exposed by processing specific SIP messages, grab them with ngrep or save in a pcap file, then add them next, or attach to issue, or provide a link to download them (e.g., to a pastebin site). -->

``` Session Initiation Protocol (SIP as raw text) REGISTER sip:mtas.ims.mnc001.mcc001.3gppnetwork.org SIP/2.0 Via: SIP/2.0/UDP 172.22.0.20:6060;branch=z9hG4bK1f1a.2acf13e0000000000000000000000000.0 To: sip:001010000084710@ims.mnc001.mcc001.3gppnetwork.org From: sip:scscf.ims.mnc001.mcc001.3gppnetwork.org;tag=577487a47557db6ca47545080fcdadff-3e5eb954 CSeq: 10 REGISTER Call-ID: 60988901578cff95-50@172.22.0.20 Content-Length: 2374 User-Agent: Kamailio S-CSCF Event: registration Max-Forwards: 10 Expires: 600120 Path: sip:scscf.ims.mnc001.mcc001.3gppnetwork.org;lr,sip:term@pcscf.ims.mnc001.mcc001.3gppnetwork.org;lr Contact: sip:scscf.ims.mnc001.mcc001.3gppnetwork.org P-Visited-Network-ID: ims.mnc001.mcc001.3gppnetwork.org P-Access-Network-Info: 3GPP-NR-TDD;utran-cell-id-3gpp=0010100000100066C000 P-Associated-URI: <sip:0912584710@ims.mnc001.mcc001.3gppnetwork.org, tel:0912584710>, sip:001010000084710@ims.mnc001.mcc001.3gppnetwork.org Content-Type: message/sip

REGISTER sip:scscf.ims.mnc001.mcc001.3gppnetwork.org:6060 SIP/2.0 From: sip:001010000084710@ims.mnc001.mcc001.3gppnetwork.org;tag=114776405 To: sip:001010000084710@ims.mnc001.mcc001.3gppnetwork.org CSeq: 114776123 REGISTER Call-ID: 114776122_989640048@192.168.101.3 Via: SIP/2.0/UDP 172.22.0.19:4060;branch=z9hG4bKc18d.4d94d35bf6f42b8e538cf9d84cb693d8.0;i=1 Via: SIP/2.0/TCP 172.22.0.21;branch=z9hG4bKc18d.8969a1b752d8220823a5bd82c9199eb9.0;i=7 Via: SIP/2.0/TCP 192.168.101.3:44186;rport=42756;branch=z9hG4bK1511394995 Max-Forwards: 67 […]Contact: sip:3259ecc0-e957-4a46-a046-8e9cab307031@192.168.101.3:44186;alias=192.168.101.3~42756~2;+g.3gpp.accesstype="cellular2";+sip.instance="urn:gsma:imei:86401006-018500-0";audio;+g.3gpp.nw-init-ussi;+g.3gpp.smsip;video;+g.3g P-Access-Network-Info: 3GPP-NR-TDD;utran-cell-id-3gpp=0010100000100066C000 Security-Verify: ipsec-3gpp;q=0.1;prot=esp;mod=trans;spi-c=4098;spi-s=4099;port-c=5101;port-s=6101;alg=hmac-sha-1-96;ealg=null Expires: 600000 Proxy-Require: sec-agree Allow: INVITE,BYE,CANCEL,ACK,NOTIFY,UPDATE,PRACK,INFO,MESSAGE,OPTIONS […]Authorization: Digest username="001010000084710@ims.mnc001.mcc001.3gppnetwork.org",realm="ims.mnc001.mcc001.3gppnetwork.org",uri="sip:ims.mnc001.mcc001.3gppnetwork.org",qop=auth,nonce="ferAjDMunr0os568G1AocOd/sdY+MoAA+PTh/ISdKLo=",nc User-Agent: Xiaomi_Redmi Note 12 5G_OS2.0.1.0.UMQEUXM […]Security-Client: ipsec-3gpp; alg=hmac-md5-96; ealg=des-ede3-cbc; spi-c=4176830254; spi-s=4255578078; port-c=42756; port-s=44186,ipsec-3gpp; alg=hmac-md5-96; ealg=aes-cbc; spi-c=4176830254; spi-s=4255578078; port-c=42756; port-s=44186 Content-Length: 0 Path: sip:term@pcscf.ims.mnc001.mcc001.3gppnetwork.org;lr Supported: path Require: path P-Visited-Network-ID: ims.mnc001.mcc001.3gppnetwork.org

```

### Possible Solutions

<!-- If you found a solution or workaround for the issue, describe it. Ideally, provide a pull request with a fix. -->

### Additional Information

* **Kamailio Version** - output of `kamailio -v`

Used in the test :

``` version: kamailio 6.1.0-dev0 (x86_64/linux) ba1369 flags: USE_TCP, USE_TLS, USE_SCTP, TLS_HOOKS, USE_RAW_SOCKS, DISABLE_NAGLE, USE_MCAST, DNS_IP_HACK, SHM_MMAP, PKG_MALLOC, MEM_JOIN_FREE, Q_MALLOC, F_MALLOC, TLSF_MALLOC, DBG_SR_MEMORY, USE_FUTEX, FAST_LOCK-ADAPTIVE_WAIT, USE_DNS_CACHE, USE_DNS_FAILOVER, USE_NAPTR, USE_DST_BLOCKLIST, HAVE_RESOLV_RES, TLS_PTHREAD_MUTEX_SHARED ADAPTIVE_WAIT_LOOPS 1024, MAX_RECV_BUFFER_SIZE 262144, MAX_SEND_BUFFER_SIZE 262144, MAX_URI_SIZE 1024, BUF_SIZE 65535, DEFAULT PKG_SIZE 8MB poll method support: poll, epoll_lt, epoll_et, sigio_rt, select. id: ba1369 compiled on 22:21:16 Mar 18 2025 with gcc 9.4.0

[scscf.log](https://github.com/user-attachments/files/20852988/scscf.log)

[kamailio_wrong_PAU.zip](https://github.com/user-attachments/files/20852989/kamailio_wrong_PAU.zip)

```

* **Operating System**:

<!-- Details about the operating system, the type: Linux (e.g.,: Debian 8.4, Ubuntu 16.04, CentOS 7.1, ...), MacOS, xBSD, Solaris, ...; Kernel details (output of `lsb_release -a` and `uname -a`) -->

``` Kamailio runs in Docker, with the following info from the container:

Distributor ID: Ubuntu Description: Ubuntu 20.04.6 LTS Release: 20.04 Codename: focal

Linux 2b805b1de581 6.8.0-62-generic #65-Ubuntu SMP PREEMPT_DYNAMIC Mon May 19 17:15:03 UTC 2025 x86_64 x86_64 x86_64 GNU/Linux

```