Custom rules UI is currently limited to transforming user patterns. There are several use cases where more advanced customization is required:

- host transform - without adding a new gateways
- ability to specify: headerparams, urlparams and fieldprams
- arbitrary url transform
- ability to specify if the rule is a mapping rule or fallback rule (currently rules with gateways are fallback rules, rules without gateways are mapping rules)

For example one should be able to define (in UI only) the following transformation:

  <userMatch>
      <description>external autoattendant</description>
      <userPattern>100</userPattern>
      <userPattern>operator</userPattern>
      <userPattern>0</userPattern>
      <permissionMatch>
        <transform>
            <user>IVR</user>
            <host>${AUTOATTENDANT_ADDR}:${AUTOATTENDANT_SIP_PORT}</host>
            <urlparams>application=auto_attendant</urlparams>
        </transform>
      </permissionMatch>
    </userMatch>