Node.js nforce connection error with Slack client Id

Question

I am in the process of creating a Slack-Salesforce chat bot, and I am currently using node.js and nforce to achieve this.

I have the following code snippet for connecting to Salesforce:

let org = nforce.createConnection ({
    clientId: SLACK_CLIENT_ID,
    clientSecret: SLACK_CLIENT_SECRET,
    redirectUri: 'http://localhost:3000/oauth/_callback',
    mode: 'single',
    autoRefresh: true
});

let login = () => {
    org.authenticate({username: SF_USER_NAME, password: SF_PASSWORD}, err => {
        if (err) {
            console.error("Authentication error");
            console.error(err);
        } else {
            console.log("Authentication successful");
        }
    });
}

However, I received an error invalid_client_id - client identifier invalid when I called the login method. The client Id is the Id provided by Slack when I installed by chat bot, so I am not sure why it is not working. It would be great if someone can help me out with this. Thanks.