Token_Issue_Token.js

const issue_access_token = async() => {
    let params = {
        grant_type: 'client_credentials',
        client_id: CHANNEL_ID,
        client_secret: CHANNEL_SECRET
    };

    let formData = querystring.stringify(params);
    let contentLength = formData.length;

    let promise = new Promise(resolve => {
        request.post({
            url: `${LINE_OAUTH_API}/accessToken`,
            headers: {
                'Content-Length': contentLength,
                'Content-Type': 'application/x-www-form-urlencoded'
            },
            body: formData
        }, (error, response, body) => {
            if(!error)
                resolve(body);
            else 
                resolve(error);
        })
    });

    let result = await promise;
    return result;

};