Blog Operation on kenji.blog

How to post a message to Slack using Slack App + OAuth2

Wed, 16 Jul 2025 23:36:27 +0900

✅ Posting Method Using an Access Token (Slack Web API)

Slack’s “OAuth Token (such as xoxb-…)” is a key used to post using Slack’s Web API. In this case, unlike Webhooks, you POST to the Slack API Endpoint with an Authorization: Bearer header.

🔑 Required Prerequisites

You need to include chat:write in the OAuth Scopes of your Slack app:

Setup Steps

Go to https://api.slack.com/apps
Create an app or select an existing one
Under “OAuth & Permissions” > Scopes → Add chat:write
“Install to Workspace” or “Reinstall” to get the Access Token (e.g., xoxb-xxxxxxxxxx)

💻 C++ Code (Posting to Slack API using WinHTTP)

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

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

bool PostSlackMessage(const std::wstring& accessToken, const std::string& channel, const std::string& text) {
 const wchar_t* host = L"slack.com";
 const wchar_t* path = L"/api/chat.postMessage";

 HINTERNET hSession = WinHttpOpen(L"SlackPoster/1.0",
 WINHTTP_ACCESS_TYPE_DEFAULT_PROXY,
 WINHTTP_NO_PROXY_NAME,
 WINHTTP_NO_PROXY_BYPASS, 0);
 if (!hSession) return false;

 HINTERNET hConnect = WinHttpConnect(hSession, host, INTERNET_DEFAULT_HTTPS_PORT, 0);
 if (!hConnect) return false;

 HINTERNET hRequest = WinHttpOpenRequest(hConnect, L"POST", path,
 NULL, WINHTTP_NO_REFERER,
 WINHTTP_DEFAULT_ACCEPT_TYPES,
 WINHTTP_FLAG_SECURE);

 // Authorization header and Content-Type
 std::wstring headers = L"Content-Type: application/json\r\n";
 headers += L"Authorization: Bearer " + accessToken + L"\r\n";

 // JSON body
 std::string body = R"({"channel":")" + channel + R"(","text":")" + text + R"("})";

 BOOL result = WinHttpSendRequest(hRequest,
 headers.c_str(),
 (DWORD)-1,
 (LPVOID)body.c_str(),
 body.length(),
 body.length(),
 0);

 if (!result || !WinHttpReceiveResponse(hRequest, NULL)) {
 std::cerr << "Send error\n";
 return false;
 }

 // Check status code
 DWORD statusCode = 0;
 DWORD size = sizeof(statusCode);
 WinHttpQueryHeaders(hRequest,
 WINHTTP_QUERY_STATUS_CODE | WINHTTP_QUERY_FLAG_NUMBER,
 WINHTTP_HEADER_NAME_BY_INDEX,
 &statusCode, &size, WINHTTP_NO_HEADER_INDEX);

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

 return (statusCode == 200);
}

int main() {
 std::wstring token = L"xoxb-your-access-token"; // Access Token
 std::string channel = "channel-ID-or-#general"; // Example: "#general" or "C0123456789"
 std::string message = "I tried posting to Slack from C++!";

 if (PostSlackMessage(token, channel, message)) {
 std::cout << "Post successful!\n";
 } else {
 std::cerr << "Post failed.\n";
 }

 return 0;
}

📌 How to Get the Channel ID

Using just the channel name (e.g., #general) may sometimes result in an error. A more reliable method is to use the ID found in the URL of the Slack channel page.

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https://app.slack.com/client/Txxxxx/C0123456789
 ↑ This part is the Channel ID

✅ About Token Types (Supplementary)

Token Format	Purpose	Example Use Case
`xoxb-...`	Bot Token (Recommended)	Post, edit, delete
`xoxp-...`	User Token (Not Recommended)	Non-bot operations
Refresh Token	Long-term token renewal	Usually not used

📝 Summary

To post to Slack from C++, the Slack Web API + Bearer Token method is reliable.
Use the chat.postMessage endpoint with HTTPS POST.
The token must be sent in the Bearer header.
Specifying the channel by ID is recommended.

Cool Web Page Templates (html5up)

Mon, 17 Apr 2023 00:26:55 +0900

Cool Web Page Templates

html5up https://html5up.net/

I wanted to try using this, so this is a memo.

[HUGO] Display Preview in Local Environment

Mon, 05 Sep 2022 12:28:01 +0900

Installing HUGO

Download

Download HUGO

From the site above, download and extract the Windows module that matches your environment. In my case, I downloaded “hugo_0.102.3_Windows-64bit.zip”.

Extract

Extract the downloaded zip file and copy the hugo.exe inside it to a folder, for example, C:\bin.

Register to Environment Variables

Register it to the environment variables so that you can run hugo.exe from anywhere. This is the operation on Windows 11, but I think it can be registered with the following steps.

Press Win+Pause to open the About page
Click Advanced system settings
Click Environment Variables
Select Path and click Edit
Click New, enter “C:\bin” on a new line, and click OK to close the dialog

Preview the Blog

In the command prompt, navigate to your HUGO blog folder and run the following command.

hugo server -D

The execution result is as follows. (The -D option is for displaying draft articles.)

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C:\Users\win11\IdeaProjects\kenji.blog>hugo server -D
Start building sites …
hugo v0.102.3-b76146b129d7caa52417f8e914fc5b9271bf56fc windows/amd64 BuildDate=2022-09-01T10:16:19Z VendorInfo=gohugoio

 | JA
-------------------+-----
Pages | 39
Paginator pages | 0
Non-page files | 7
Static files | 0
Processed images | 0
Aliases | 13
Sitemaps | 1
Cleaned | 0

Built in 161 ms
Watching for changes in C:\Users\win11\IdeaProjects\kenji.blog\{archetypes,content,themes}
Watching for config changes in C:\Users\win11\IdeaProjects\kenji.blog\config.toml
Environment: "development"
Serving pages from memory
Running in Fast Render Mode. For full rebuilds on change: hugo server --disableFastRender
Web Server is available at http://localhost:1313/ (bind address 127.0.0.1)
Press Ctrl+C to stop

The address will be output when executed (in the example above, http://localhost:1313/), so copy the address to your browser. The preview will automatically update every time you save a file. To end the preview, press Ctrl+C in the command prompt.