feat: Add the possibility to manipulate query parameters / search string using proxy-rewrite plugin

[markokocic]

Description

proxy-rewrite plugin has a possibility to add / remove / set headers to the request. It would be nice if it were possible to add / remove / set url query parameters.

For example, let's say we get a request with the following uri: /path?param1=1&param2=this&param3=that and want to overwrite param1, remove param2, and add param4 before sending the request to the upstream. If proxy-rewrite would have the same options for query params as for headers, we could configure it somethign like this:

 "proxy-rewrite": {
    "uri": "/test/home.html",
    "host": "iresty.com",
    "query-params": {
       "set": {
            "param1": "etwas"
        },
        "add": {
            "param4": "(id=32&name=\"test*\")&age<32",
            "param4" : "it's valid to have more params with the same name"
        },
        "remove":[
            "param2"
        ]
    }

Plugin should take care that complete search sting is properly escaped and encoded. This would come very handy when dealing with ODATA services on the backend that use query-params intensively.

Alternative: theoretically it is possible to manipulate the whole uri, including the search string, using regex_uri, but in the case of multiple parameters that regex can quickly grow very wild and unreliable.

[kayx23]

Just adding that the plugin currently can add URI parameters by rewriting the whole URI. See example here: https://docs.api7.ai/hub/proxy-rewrite#add-url-parameters

It does not yet support the capability to rewrite each URI parameter individually as @markokocic mentioned.