How to build a public Smartsheet integration: Building the Auth Flow

Hey there, fellow JavaScript developer! Ready to dive into the world of Smartsheet integrations? Today, we're going to focus on one of the most crucial parts of building a public integration: the authorization flow. Don't worry, it's not as daunting as it sounds, and I'll walk you through it step by step.

Introduction

Smartsheet's API is a powerful tool that allows us to interact with their platform programmatically. But before we can start pulling in data or making changes, we need to make sure our integration is secure and authorized. That's where the auth flow comes in.

Prerequisites

Before we jump in, make sure you've got:

• A Smartsheet developer account (if you don't have one, go grab one real quick)
• A registered application in Smartsheet (you'll need this for the client ID and secret)

Got those? Great! Let's get started.

OAuth 2.0 Flow Overview

We'll be using the OAuth 2.0 authorization code grant type. It's a bit more complex than simple API keys, but it's much more secure and flexible for user-facing integrations.

Implementing the Authorization Flow

Initiating the Authorization Request

First things first, we need to send our users to Smartsheet to grant permissions. Here's how we construct the URL:

const authUrl = `https://app.smartsheet.com/b/authorize?response_type=code&client_id=${YOUR_CLIENT_ID}&scope=${SCOPES}&state=${STATE}`;

Replace YOUR_CLIENT_ID with your actual client ID, SCOPES with the permissions you need, and STATE with a random string to prevent CSRF attacks.

Now, redirect your user to this URL. They'll log in to Smartsheet and grant permissions to your app.

Handling the Callback

Once the user grants permission, Smartsheet will redirect them back to your specified callback URL with an authorization code. Here's how you might handle that in Express:

app.get('/callback', (req, res) => {
  const { code, state } = req.query;
  
  // Validate state to prevent CSRF attacks
  if (state !== expectedState) {
    return res.status(400).send('Invalid state parameter');
  }
  
  // Exchange code for access token (we'll do this next)
});

Exchanging the Code for Access Token

Now for the fun part! Let's exchange that code for an access token:

const axios = require('axios');

const tokenResponse = await axios.post('https://api.smartsheet.com/2.0/token', {
  grant_type: 'authorization_code',
  client_id: YOUR_CLIENT_ID,
  client_secret: YOUR_CLIENT_SECRET,
  code: code
});

const { access_token, refresh_token } = tokenResponse.data;

Make sure to securely store these tokens. The access token is what you'll use to make API calls, and the refresh token... well, that brings us to our next step.

Refreshing the Access Token

Access tokens don't last forever. When they expire, you'll need to use the refresh token to get a new one:

const refreshResponse = await axios.post('https://api.smartsheet.com/2.0/token', {
  grant_type: 'refresh_token',
  client_id: YOUR_CLIENT_ID,
  client_secret: YOUR_CLIENT_SECRET,
  refresh_token: stored_refresh_token
});

const { access_token, refresh_token } = refreshResponse.data;

Remember to update your stored tokens after refreshing!

Security Considerations

Security is crucial when dealing with auth flows. Here are some key points:

• Always use HTTPS
• Store tokens securely (consider encryption for added security)
• Implement CSRF protection (that's what the state parameter is for)

Error Handling

OAuth can throw some curveballs. Be prepared to handle errors like:

• Invalid grant
• Invalid client
• Access denied

Always provide clear error messages to your users and log detailed errors for debugging.

Testing the Authorization Flow

Before you ship it, test it! Here's a quick checklist:

1. Initiate the auth flow
2. Grant permissions on Smartsheet
3. Handle the callback and exchange the code
4. Make an API call with the access token
5. Let the access token expire and test the refresh flow

Consider setting up automated tests for ongoing reliability.

Conclusion

And there you have it! You've just built a secure authorization flow for your Smartsheet integration. Pat yourself on the back – this is often the trickiest part of building an integration.

From here, you're all set to start making API calls and building out the rest of your integration. Remember, the Smartsheet API docs are your friend if you get stuck.

Happy coding, and may your API calls always return 200 OK!