build-message-card.cs

private async Task ProcessAsync(string webhookUri, string summary, string title = null, string text = null, string themeColor = null, string sections = null, string actions = null)
{
    var card = new MessageCard()
    {
        Title = title,
        Summary = summary,
        Text = text,
        ThemeColor = themeColor,
        Sections = ParseCollection<Section>(sections),
        Actions = ParseCollection<BaseAction>(actions)
    };

    var converted = JsonConvert.SerializeObject(card, settings);

    var message = (string)null;
    var requestUri = webhookUri;

    using (var client = new HttpClient())
    using (var content = new StringContent(converted, Encoding.UTF8, "application/json"))
    using (var response = await client.PostAsync(requestUri, content).ConfigureAwait(false))
    {
        response.EnsureSuccessStatusCode();
    }
}

private List<T> ParseCollection<T>(string value)
{
    var parsed = string.IsNullOrWhiteSpace(value)
                 ? null
                 : JsonConvert.DeserializeObject<List<T>>(value, settings);

    return parsed;
}

console-app.cs

public static void Main(string[] args)
{
    var webhookUri = args[0];
    var summary = args[1];
    var title = args[2];
    var text = args[3];
    var themeColor = args[4];
    var sections = args[5];
    var actions = args[6];

    ProcessAsync(
        webhookUri,
        summary,
        title,
        text,
        themeColor,
        sections,
        actions).Result;
}

function-app.cs

[FunctionName("SendMessageHttpTrigger")]
public static async Task<IActionResult> Run(
    [HttpTrigger(AuthorizationLevel.Function, "post", Route = "teams/send")] HttpRequest req,
    ILogger log)
{
    log.LogInformation("C# HTTP trigger function processed a request.");

    var body = await new StreamReader(req.Body).ReadToEndAsync().ConfigureAwait(false);
    dynamic payload = JsonConvert.DeserializeObject<object>(body);

    await ProcessAsync(
        payload.webhookUri,
        payload.summary,
        payload.title,
        payload.text,
        payload.themeColor,
        payload.sections,
        payload.actions).ConfigureAwait(false);

    return new OkResult();
}