API Auth: Do you Need it? And its Parts

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Before we dive into the code, we need to have a heart-to-heart about API authentication. Because... I think there's some confusion out there that tends to make people over-complicate things. And I never want to over-complicate things.

Do you Need API Authentication

First, you need to ask yourself a very important question:

Do you actually need an API token authentication system?

There's a pretty good chance that the answer is... no, even if your app has API endpoints:

... lines 1 - 11
class AccountController extends BaseController
{
... lines 14 - 24
/**
* @Route("/api/account", name="api_account")
*/
public function accountApi()
{
... lines 30 - 31
return $this->json($user, 200, [], [
'groups' => ['main'],
]);
}
}

If you're creating API endpoints solely so that your own JavaScript for your own site can use them, then, you do not need an API token authentication system. Nope! Your life will be much simpler if you use a normal login form and session-based authentication.

Yep! You probably already know, that, once you login via a login form, you can instantly make authenticated AJAX requests from JavaScript, because those requests send the session cookie. So, if the only thing that needs to use your API is your own JavaScript, just use LoginFormAuthenticator.

Oh, and if you need to be fancier with your login form, sure! You can totally use JavaScript to make the login form submit via AJAX. Nothing would need to change in your authenticator, except that you would probably want to send back JSON on success, instead of redirecting:

... lines 1 - 19
class LoginFormAuthenticator extends AbstractFormLoginAuthenticator
{
... lines 22 - 74
public function onAuthenticationSuccess(Request $request, TokenInterface $token, $providerKey)
{
if ($targetPath = $this->getTargetPath($request->getSession(), $providerKey)) {
return new RedirectResponse($targetPath);
}
return new RedirectResponse($this->router->generate('app_homepage'));
}
... lines 83 - 87
}

You would also override onAuthenticationError() and the start() method to do the same. We'll learn more about those methods soon.

Of course, even if your JavaScript will be the only thing using your API, you can still build an API token authentication system, if you want. And if you need other things to be able to access your API, then you need a token system.

Two Sides of API Token Authentication

If you're still here, then you've either decided that you do need an API token authentication system, or you just want to nerd out with us on this topic. Me too!

This brings us to important topic number 2! An API token authentication system has two, quite unrelated parts. The first is how your app processes an existing API token and logs in the user. The second is how those API tokens are created and distributed.

Part 1: Processing an API Token

For the first part, no matter how you build it, an API token is just a string that is somehow connected to a User in your system. The client that makes the request sets the token string on a header and then they become authenticated as that User. There are some variations on this, like, giving tokens "scopes" or "permissions" so that they can only do some things that a user can do, but that's the basic idea.

The way that the token string is related to the user can be done in a few different ways. For example, you could have an API token database table where each random API token has a relationship to a row in the user table. It's simple: our app reads the token string from a header, finds that API token in the database, finds the User it's related to, and authenticates as that user. We're going to build exactly this.

Another variation is JSON web tokens. In this case, instead of the token being a random string, the user's information - like the user id - is used to create a signed string. In that case, your app reads the header, verifies the signature on the string, and uses the id inside that string to query for the User.

Anyways, that is the first part of API token authentication: designing your app to be able to read API tokens from an API request, and use that information - somehow - to find the correct User and authenticate them.

Part 2: Creating & Distributing API Tokens

The second part of an API authentication system asks this question:

How are these API tokens created and distributed?

It turns out that this is a totally separate conversation. And, once again, there are several valid answers. I'll give you 3 examples with when each should probably be used. Actually, the GitHub API is an example of a system that allows you to do all three of these.

First, you could allow API tokens to be created through a web interface. Like, a user logs in, they navigate to some API token page, and then they create one or more API tokens that are tied to their account. This solution is dead simple. The negative is that there is no automated way to create an API token: you can't write a script that can create them. It must be done manually.

Second, you could write an API endpoint whose jobs is to create & return tokens. In this example, you would send your email & password to the API endpoint, it would validate them, then create & return the token. This is still pretty simple, but now it's programmable: you can write a script that can create tokens on its own. The downside is that this solution can't be used by third parties. What I mean is, it's okay for the user to write some code that sends their own email and password to an API endpoint in order to create a token. But, if some third-party were building an iPhone app for your site, that app should not use this method. Why? Because it would require the user to enter their email & password directly into the app, so that it could send the info to our API. Ideally, we never want users to give their password to a third-party.

This leads us to the third way of creating & distributing tokens: OAuth2. If you need third-parties to be able to securely create & get API tokens for your users, then you probably need OAuth. The only negative is that OAuth is more complex.

Phew! So, the whole second part of API token authentication... well, really has nothing to do with authentication at all! It's more about how these secrets keys are created and handed out to who needs them. So, we are not going to talk about that part of API authentication.

But we are going to build the first part: the true authentication part. Let's get to work!

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What PHP libraries does this tutorial use?

// composer.json
{
    "require": {
        "php": "^7.1.3",
        "ext-iconv": "*",
        "knplabs/knp-markdown-bundle": "^1.7", // 1.7.0
        "knplabs/knp-paginator-bundle": "^2.7", // v2.8.0
        "knplabs/knp-time-bundle": "^1.8", // 1.8.0
        "nexylan/slack-bundle": "^2.0,<2.2.0", // v2.0.0
        "php-http/guzzle6-adapter": "^1.1", // v1.1.1
        "sensio/framework-extra-bundle": "^5.1", // v5.2.0
        "stof/doctrine-extensions-bundle": "^1.3", // v1.3.0
        "symfony/asset": "^4.0", // v4.1.4
        "symfony/console": "^4.0", // v4.1.4
        "symfony/flex": "^1.0", // v1.2.7
        "symfony/framework-bundle": "^4.0", // v4.1.4
        "symfony/lts": "^4@dev", // dev-master
        "symfony/orm-pack": "^1.0", // v1.0.6
        "symfony/security-bundle": "^4.0", // v4.1.4
        "symfony/serializer-pack": "^1.0", // v1.0.1
        "symfony/twig-bundle": "^4.0", // v4.1.4
        "symfony/web-server-bundle": "^4.0", // v4.1.4
        "symfony/yaml": "^4.0", // v4.1.4
        "twig/extensions": "^1.5" // v1.5.2
    },
    "require-dev": {
        "doctrine/doctrine-fixtures-bundle": "^3.0", // 3.0.2
        "easycorp/easy-log-handler": "^1.0.2", // v1.0.7
        "fzaninotto/faker": "^1.7", // v1.8.0
        "symfony/debug-bundle": "^3.3|^4.0", // v4.1.4
        "symfony/dotenv": "^4.0", // v4.1.4
        "symfony/maker-bundle": "^1.0", // v1.7.0
        "symfony/monolog-bundle": "^3.0", // v3.3.0
        "symfony/phpunit-bridge": "^3.3|^4.0", // v4.1.4
        "symfony/profiler-pack": "^1.0", // v1.0.3
        "symfony/var-dumper": "^3.3|^4.0" // v4.1.4
    }
}