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OAuth Applications

If you want to do some API requests on behalf of another user, you need to register an OAuth application.

For example, you might be creating a website that processes someone’s itch.io data in some way.

Or, you want to use the itch.io API in your game even when it’s launched without the itch.io app.

Tip: If you just want to use the itch.io API in your game, you can simply add the API scopes you need in your app manifest.

It’s by far the easiest for you to set up, and the best user experience for your players!

Introduction

The API documented in this page implements the “Implicit flow” of the OAuth 2.0 spec. If you're already familiar with it, you should only need to skim through the page and pick the implementation details you need.

In short, the OAuth 2.0 implicit flows works like this:

  • You redirect the user to https://itch.io/user/oauth
    • This is where you pass your client ID and the scope you need
  • The user sees a page where they can review the permissions (scopes) you're asking for.
  • If they accept, credentials for your app are generated and the user is redirected to the Authorization Callback URL you specified when registering the OAuth app. This is a page you control and you serve.
  • The credentials you need are included in the hash part of the URL.
    • The callback page you serve should include javascript code that extracts the access token you need and POSTs it securely to your server

Registering an OAuth application

As a developer, you can manage your OAuth applications from your user settings.

Try to keep things neat and tidy. If you have multiple websites or games using the itch.io API for a different purpose, create separate OAuth apps for them.

The authorization step

To let users choose to grant permissions to your apps, you should redirect them to the following address:

https://itch.io/user/oauth

It requires the following parameters:

  • client_id: The Client ID corresponding to your OAuth application, which you can retrieve from your OAuth application settings
  • scope: A space-separated list of scopes you'd like access to (see the Scopes section below)
  • redirect_uri: The address of a page the user will be redirected to if they accept to grant your app permissions. This must match your OAuth application settings. See the Redirect URI section below.
  • state (optional): If this is specified, it will be included in the hash part of the address the user is redirected to. See the Security Considerations section below.

The parameters should be included as a query string. Here’s a sample authorization URL with dummy values:

https://itch.io/user/oauth?client_id=foobar&scope=profile:me&redirect_uri=https%3A%2F%2Fexample.org%2F

Scopes

The only scope you can request is profile:me. It gives you access to the /me API endpoint. In the future, as we expand the API, we will make more scopes available. Need something specific? Get in touch.

See the server-side documentation for a list of endpoints and their scopes.

Redirect URIs

The redirect URI (or Authorization callback address) is where a user will get redirected after they approve your request for credentials.

The credentials are included in the hash part of the URL.

For example, if you specify the following redirect URL:

https://example.org/oauth/callback?a=b

Then the user will get redirected to the following page:

https://example.org/oauth/callback?a=b#access_token=YYY&state=ZZZ

The hash part of the URL is encoded like a query string – see the next section for retrieval.

Loopback address (local http server)

If you're creating a desktop application, you may have to set the redirect URI to the loopback address, like http://127.0.0.1:34567.

Out-of-band authentication (copy/paste)

If you set the redirect URI to urn:ietf:wg:oauth:2.0:oob, the user won’t be redirected. Instead they'll be shown a page with the API key and instructions to copy and paste it into your app.

This is especially useful in scenarios where:

  • You set the redirect URI to a loopback address
  • …but were not able to listen on that address
    • either because some other program was already listening on that poart
    • or because the user did not allow your program to listen on a port (the Windows firewall will do that)

So, as a best practice, if you're implementing a desktop app, you should try to listen on your registered loopback address, and if you can’t, fall back to urn:ietf:wg:oauth:2.0:oob and allow your user to copy & paste the API key instead.

Retrieving the access token in JavaScript

The hash part of URLs is not seen by HTTP servers, or HTTP proxies. That’s why the OAuth 2.0 Implicit Flow puts sensitive information (the access token) in there.

That means you need to serve a page that includes a bit of JavaScript to retrieve the access token, and send it to your server, usually via an XHR).

It’s tempting to use a couple of regular expressions to retrieve the access token, but we encourage you to use libraries or standard APIs instead.

Here is example code to retrieve the access_token:

// this code assumes a recent browser or polyfill - see next paragraphs

// first, remove the '#' from the hash part of the URL
var queryString = window.location.hash.slice(1);
var params = new URLSearchParams(queryString);
var accessToken = params.get("access_token");

// you can also get the state param if you're using it:
var state = params.get("state");

See this code in action in this codepen

URLSearchParams is available in recent browsers, see the ‘Browser compatibility’ section of URLSearchParams’s MDN page.

If you need to support older browsers, you can use a polyfill: url-search-params comes with a build you can easily include in your website.

Using the access token

Once you've successfully extracted the access token from the hash part of the URL, posted it to your server with an XHR, and saved it in your database, you can use it to make API requests.

Access tokens given by the OAuth 2.0 flow are API keys, which you can use as described in the server-side API docs.

Checking the access token’s permissions

You can use the /credentials/info endpoint to list the scopes associated with an access token. Look it up in the server-side API docs for details.

Security considerations

To avoid various types of attack, the OAuth 2.0 spec recommends only requesting the scopes you need:

  • Be specific: if all you need is profile:me, don’t request all of profile
  • If you need more permissions later, you can always make the user go through the flow again to expand the scope of your credentials.

We only support the profile:me scope right now, but as we expand the API you'll be able to request more scopes.

The OAuth Authorization callback page should be served over HTTPS to avoid man-in-the-middle attacks. Nowadays, getting an SSL certificate is easy thanks to efforts like Let’s Encrypt

The OAuth Authorization callback page should not include any third-party javascript code (social sharing widgets, etc.) – if it does, you should at least make sure your access token extraction code runs first and that it clears window.location.hash.

A state parameter can be used as a nonce – it is generated by your server, included in the login URL, and then again in the callback URL as part of the hash. You should check that the value you get back is equal to the one you passed in.