identity
========

Use the identity API to get an OAuth2 authorization code or access token, which an extension can then use to access user data from a service that supports OAuth2 access (such as Google or Facebook).

OAuth2 flows vary between service provider so, to use this API with a particular service provider, consult their documentation. For example:

* Google
* GitHub

The identity API provides the `identity.launchWebAuthFlow()` function. This authenticates the user with the service, if necessary, and asks the user to authorize the extension to access data, if necessary. The function completes with an access token or authorization code, depending on the provider.

The extension then completes the OAuth2 flow to get a validated access token, and uses the token in HTTPS requests to access the user's data according to the authorization the user gave.

To use this API, you must have the "identity" API permission.

Setup
-----

There's some setup you must do before publishing your extension.

### Getting the redirect URL

The redirect URL represents the end point of `identity.launchWebAuthFlow()`, in which the access token or authorization code is delivered to the extension. The browser extracts the result from the redirect URL without loading its response.

You get the redirect URL by calling `identity.getRedirectURL()`. This function derives a redirect URL from the add-on's ID. To simplify testing, set your add-on's ID explicitly using the `browser_specific_settings` key (otherwise, each time you temporarily install the add-on, you get a different redirect URL).

`identity.getRedirectURL()` returns a URL at a fixed domain name and a subdomain derived from the add-on's ID. Some OAuth servers (such as Google) only accept domains with a verified ownership as the redirect URL. As the dummy domain cannot be controlled by extension developers, the default domain cannot always be used.

However, loopback addresses are an accepted alternative that do not require domain validation (based on RFC 8252, section 7.3). Starting from Firefox 86, a loopback address with the format `http://127.0.0.1/mozoauth2/[subdomain of URL returned by identity.getRedirectURL()]` is permitted as a value for the redirect URL.

**Note:** Starting with Firefox 75, you must use the redirect URL returned by `identity.getRedirectURL()`. Earlier versions allowed you to supply any redirect URL.

Starting with Firefox 86, the special loopback address described above can be used too.

You'll use the redirect URL in two places:

* supply it when registering your extension as an OAuth2 client.
* pass it into `identity.launchWebAuthFlow()`, as a URL parameter added to that function's `url` argument.
### Registering your extension

Before you use OAuth2 with a service provider, you must register the extension with the provider as an OAuth2 client.

This will tend to be specific to the service provider, but in general it means creating an entry for your extension on the provider's website. In this process you supply your redirect URL, and receive a client ID (and sometimes also a secret). You need to pass both of these into `identity.launchWebAuthFlow()`.

Functions
---------

`identity.getRedirectURL()`

Gets the redirect URL.

`identity.launchWebAuthFlow()`

Launches WAF.

Browser compatibility
---------------------

BCD tables only load in the browser with JavaScript enabled. Enable JavaScript to view data.

Example extensions
------------------

* google-userinfo

**Note:** This API is based on Chromium's `chrome.identity` API.