Spotify.NET/SpotifyAPI.Docs/docs/SpotifyWebAPI/proxy.md

Proxy Settings

You can forward your proxy settings to the web api by using a field in the SpotifyLocalAPIConfig.

ProxyConfig proxyConfig = new ProxyConfig() 
{
    Host = "127.0.0.1",
    Port = 8080
    // Additional values like Username and Password are available
};

SpotifyWebAPI api = new SpotifyWebAPI(proxyConfig);
// or
WebAPIFactory webApiFactory = new WebAPIFactory(..., proxyConfig);
SpotifyWebAPI api = await webApiFactory.GetWebApi();