Extract parameter from request and return external URL using it

I want to capture a URL with a parameter and return an external site having the parameter as part of its URL. To simplify, I want this:

/google/<something> -> https://www.google.com/?q=<something>

How can I achieve this with Yarp?

You can use QueryRouteParameter: to set the route parameter as a query parameter. Here is an example for your reference:

{
  "ReverseProxy": {
    "Routes": {
      "route1": {
        "ClusterId": "cluster1",
        "Match": {
          "Path": "/WeatherForecast/PP/{**remainder}"
        },
        "Transforms": [
          {
            "PathRemovePrefix": "/WeatherForecast/PP"
          },
          {
            "PathSet": "/WeatherForecast/PP/"
          },
          {
            "QueryRouteParameter": "q",
            "Set": "remainder"
          }
        ]
      }
    },
    "Clusters": {
      "cluster1": {
        "Destinations": {
          "destination1": {
            "Address": "https://localhost:7258"
          }
        }
      }
    }
  }
}

In this example, I set remainder as a query parameter:https://localhost:7258/WeatherForecast/PP as my target address. When I enter https://localhost:7247/WeatherForecast/PP/3 in the URL

It will jump to my target address:

Update

{
  "ReverseProxy": {
    "Routes": {
      "route1": {
        "ClusterId": "cluster1",
        "Match": {
          "Path": "/google/{**remainder}"
        },
        "Transforms": [
          {
            "PathRemovePrefix": "/google"
          },
          {
            "PathSet": "/"
          },
          {
            "QueryRouteParameter": "q",
            "Set": "remainder"
          }
        ]
      }
    },
    "Clusters": {
      "cluster1": {
        "Destinations": {
          "destination1": {
            "Address": "https://www.google.com/"
          }
        }
      }
    }
  }
}

When I enter the address https://localhost:7247/google/2, I will be redirected to https://www.google.com/?q=2