kurtyks created an issue (kamailio/kamailio#4316)

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### Description

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### Expected behavior

#### Actual observed behavior

#### Debugging Data

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#### Log Messages

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#### SIP Traffic

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``` (paste your sip traffic here) ``` Rn. UAC module allows only global setting of Contact header, while sending REGISTER to UAS. It is done by setting param reg_contact_addr (string). This is edge case, but sometimes for diffrent itsp’s i need to pass diffrent contact value, while for example one is on public internet, other is behind vpn. It d be nice just to extend uacreg table + contact_addr, contact_port, contact_user or just by adding contact field with URI to be sent in register.

### Possible Solutions

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### Additional Information

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

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* **Operating System**:

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