Set GoogleGeocoder.Proxy Before Geocoding.NET Starts Its Request

var geocoder = new Geocoding.Google.GoogleGeocoder(apiKey)
{
    Proxy = new System.Net.WebProxy("http://proxy.example:8080")
    {
        Credentials = new System.Net.NetworkCredential(
            proxyUser, proxyPassword)
    }
};

Use the application's API key and intermediary account, then call GeocodeAsync or ReverseGeocodeAsync through this configured geocoder. Omit Credentials for an unauthenticated proxy. In that case, the HTTP proxy list supplies candidates when public geocoding requests are permitted through public intermediaries.

Geocoding.NET's request path creates an HttpClientHandler and assigns its public IWebProxy property. A different HttpClient configured elsewhere does not replace that route.

Keep an intermediary 407 distinct from Google's invalid-key or denied-request response. For integrated authentication, use the Windows identity/domain appropriate to that proxy rather than substituting the Maps key for a proxy password.