How to Post Messages to Microsoft Teams from C++ (WinHTTP + Graph API)

I want to automatically post to a Microsoft Teams chat –
Microsoft Graph API is exactly what you can use in such cases.
In this article, I will introduce a C++ code example using WinHTTP ** and the ** necessary API authentication steps step by step.

🔧 Necessary Preparations (Microsoft Graph API Authentication Settings)

1. Register App in Azure Portal

First, to use the Microsoft Graph API, you need to register an app in Azure.

Access the Azure Portal
“Microsoft Entra ID ” > “+ Add ” > “ App registrations ” > “ New registration”
Enter any app name and click “Register”

2. Add API Permissions

Go to the “API permissions” left menu
Under “Microsoft Graph ” > “ Add a permission ”, search for the following scopes and click “ Update permissions”

Chat.ReadWrite
User.Read

If you want to post to a channel, ChannelMessage.Send is also required

3. Note Client ID and Tenant ID

Make a note of the following two items displayed on the “Overview” tab:

Application (client) ID
Directory (tenant) ID

4. Create Client Secret

Go to the “Certificates & secrets” tab
“New client secret” > set the expiration date, and click “Add”
Be sure to note ** the displayed value (secret) ** on the spot

🔐 Obtaining an Access Token (OAuth2)

Use the client_credentials flow to obtain it.
Run the following command with curl to obtain an access token.

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curl -X POST ^
  https://login.microsoftonline.com/{tenant_id}/oauth2/v2.0/token ^
  -H "Content-Type: application/x-www-form-urlencoded" ^
  -d "client_id={client_id}" ^
  -d "scope=https%3A%2F%2Fgraph.microsoft.com%2F.default" ^
  -d "client_secret={client_secret}" ^
  -d "grant_type=client_credentials"

Example Response

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{
  "token_type":"Bearer",
  "expires_in":3599,
  "ext_expires_in":3599,
  "access_token": "eyJ0eXAiOiJKV1QiLCJub... (omitted)"
}

Call the Microsoft Graph API using this access_token.

💬 C++ Sample for Posting to Teams Chat

Here is a C++ example of posting to a chat using WinHTTP.

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#include <windows.h>
#include <winhttp.h>
#include <iostream>
#include <string>

#pragma comment(lib, "winhttp.lib")

void PostToTeamsChat(const std::wstring& accessToken, const std::wstring& chatId, const std::wstring& message) {
    HINTERNET hSession = WinHttpOpen(L"TeamsPoster/1.0", WINHTTP_ACCESS_TYPE_DEFAULT_PROXY,
                                     WINHTTP_NO_PROXY_NAME, WINHTTP_NO_PROXY_BYPASS, 0);

    HINTERNET hConnect = WinHttpConnect(hSession, L"graph.microsoft.com", INTERNET_DEFAULT_HTTPS_PORT, 0);

    std::wstring endpoint = L"/v1.0/chats/" + chatId + L"/messages";
    HINTERNET hRequest = WinHttpOpenRequest(hConnect, L"POST", endpoint.c_str(), NULL,
                                            WINHTTP_NO_REFERER, WINHTTP_DEFAULT_ACCEPT_TYPES, WINHTTP_FLAG_SECURE);

    std::wstring jsonBody = L"{\"body\": {\"content\": \"" + message + L"\"}}";
    std::wstring headers = L"Authorization: Bearer " + accessToken + L"\r\nContent-Type: application/json\r\n";

    BOOL bResult = WinHttpSendRequest(hRequest,
                                      headers.c_str(), (DWORD)-1L,
                                      (LPVOID)jsonBody.c_str(), (DWORD)(jsonBody.length() * sizeof(wchar_t)),
                                      (DWORD)(jsonBody.length() * sizeof(wchar_t)), 0);

    if (bResult)
        WinHttpReceiveResponse(hRequest, NULL);

    DWORD dwSize = 0;
    WinHttpQueryDataAvailable(hRequest, &dwSize);

    if (dwSize > 0) {
        std::wstring response(dwSize / sizeof(wchar_t), 0);
        DWORD dwDownloaded = 0;
        WinHttpReadData(hRequest, &response[0], dwSize, &dwDownloaded);
        std::wcout << L"Response: " << response << std::endl;
    }

    WinHttpCloseHandle(hRequest);
    WinHttpCloseHandle(hConnect);
    WinHttpCloseHandle(hSession);
}

int main() {
    std::wstring access;
    std::wstring chatId = L"19:";
    std::wstring message = L"Hello from C++!";
    std::wcout << L"Enter your access token: ";
    std::getline(std::wcin, access);
    std::wcout << L"Enter chat ID: ";
    std::getline(std::wcin, chatId);
    PostToTeamsChat(access, chatId, message);
    return 0;
}

🔍 How to Get Chat ID

You can check the Chat ID with GET /v1.0/me/chats.

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curl -X GET ^
  https://graph.microsoft.com/v1.0/me/chats ^
  -H "Authorization: Bearer {access_token}" ^
  -H "Content-Type: application/json"

Example Response

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{
  "value": [
    {
      "id": "19:abc123xyz@thread.v2",
      "topic": null,
      "chatType": "oneOnOne"
    }
  ]
}

📌 Points to Note

This sample is a minimal implementation. In actual operation:
- Token expiration handling
- HTTPS certificate validation
- Enhanced error handling
For channel posting, use teams/{team-id}/channels/{channel-id}/messages.
Sending attachments requires multipart processing or the Graph Drive API.

Summary

📎 Summary

Feature	Overview
Graph API	Official API to interact with Teams
App Registration	Required authentication procedures on Azure
Access Token	Obtained via OAuth2, used for requests
C++ Implementation	Call Graph API using WinHTTP

🚀 Next Steps

As more advanced samples, the following are also possible:

Team channel posting (/teams/{team-id}/channels/...)
Posting with attachments
Switching between bot accounts and user accounts
Full C++ implementation including token acquisition

If you have any requests, please feel free to comment!