I’ve been able to send a Python chat message to a google chat webhook by following the instructions provided by Google.

Now, my goal is to implement this solution in a C# application. Instead of using classic HttpClient with POST requests, I’m trying to use the official nuget packages.

How do you use the nuget library to connect with a webhook (not with credentials or API Keys) ?

using Google.Apis.HangoutsChat.v1;
using Google.Apis.HangoutsChat.v1.Data;
using Google.Apis.Services;

public class GoogleChatNotification
{
    private string _key;
    private string _token;
    private string _space_id;

    public GoogleChatNotification(string webhook)
    {
        if (webhook.IsNullOrWhiteSpace())
            throw new Exception("Webhook can't be empty");

        //Google chat webhook format : "https://chat.googleapis.com/v1/spaces/{space_id}/messages?key={key}&token={token}"
        Uri webHookUri = new Uri(webhook);
        var queryDictionary = System.Web.HttpUtility.ParseQueryString(webHookUri.Query);

        _key = queryDictionary["key"];
        _token = queryDictionary["token"];
        _space_id = webHookUri.Segments[2] + webHookUri.Segments[3].Replace("/","");
    }

    public async Task SendMessage(string message, string? threadId)
    {
        var service = new HangoutsChatService(new BaseClientService.Initializer()
        {
            ApplicationName = "MyApp",
            ApiKey = _key 
        }); //<= Throw an credential error ! How do you connect with a webhook URL ?

        var pubSubMessage = new Message
        {
            Text = message,
            Thread = new Google.Apis.HangoutsChat.v1.Data.Thread() { Name = threadId },
            Sender = new User() { Name = "MyApp Bot", DisplayName = "MyApp Bot", Type = "BOT" }
        };

        SpacesResource.MessagesResource.CreateRequest req = new SpacesResource.MessagesResource(service).Create(pubSubMessage, _space_id);
        await req.ExecuteAsync();
    }
}

Thank for you support.