Authentication

Unlike Web applications, RESTful APIs are usually stateless, which means sessions or cookies should not be used. Therefore, each request should come with some sort of authentication credentials because the user authentication status may not be maintained by sessions or cookies. A common practice is to send a secret access token with each request to authenticate the user. Since an access token can be used to uniquely identify and authenticate a user, API requests should always be sent via HTTPS to prevent man-in-the-middle (MitM) attacks.

There are different ways to send an access token:

• HTTP Basic Auth: the access token is sent as the username. This should only be used when an access token can be safely stored on the API consumer side. For example, the API consumer is a program running on a server.
• Query parameter: the access token is sent as a query parameter in the API URL, e.g., https://example.com/users?access-token=xxxxxxxx. Because most Web servers will keep query parameters in server logs, this approach should be mainly used to serve JSONP requests which cannot use HTTP headers to send access tokens.
• OAuth 2: the access token is obtained by the consumer from an authorization server and sent to the API server via HTTP Bearer Tokens, according to the OAuth2 protocol.

Yii supports all of the above authentication methods. You can also easily create new authentication methods.

To enable authentication for your APIs, do the following steps:

1. Configure the user application component:
   • Set the enableSession property to be false.
   • Set the loginUrl property to be null to show a HTTP 403 error instead of redirecting to the login page.
2. Specify which authentication methods you plan to use by configuring the authenticator behavior in your REST controller classes.
3. Implement yii\web\IdentityInterface::findIdentityByAccessToken() in your user identity class.

Step 1 is not required but is recommended for RESTful APIs which should be stateless. When enableSession is false, the user authentication status will NOT be persisted across requests using sessions. Instead, authentication will be performed for every request, which is accomplished by Step 2 and 3.

Tip: You may configure enableSession of the user application component in application configurations if you are developing RESTful APIs in terms of an application. If you develop RESTful APIs as a module, you may put the following line in the module's init() method, like the following:

public function init()
{
    parent::init();
    \Yii::$app->user->enableSession = false;
}

For example, to use HTTP Basic Auth, you may configure the authenticator behavior as follows,

use yii\filters\auth\HttpBasicAuth;

public function behaviors()
{
    $behaviors = parent::behaviors();
    $behaviors['authenticator'] = [
        'class' => HttpBasicAuth::className(),
    ];
    return $behaviors;
}

If you want to support all three authentication methods explained above, you can use CompositeAuth like the following,

use yii\filters\auth\CompositeAuth;
use yii\filters\auth\HttpBasicAuth;
use yii\filters\auth\HttpBearerAuth;
use yii\filters\auth\QueryParamAuth;

public function behaviors()
{
    $behaviors = parent::behaviors();
    $behaviors['authenticator'] = [
        'class' => CompositeAuth::className(),
        'authMethods' => [
            HttpBasicAuth::className(),
            HttpBearerAuth::className(),
            QueryParamAuth::className(),
        ],
    ];
    return $behaviors;
}

Each element in authMethods should be an auth method class name or a configuration array.

Implementation of findIdentityByAccessToken() is application specific. For example, in simple scenarios when each user can only have one access token, you may store the access token in an access_token column in the user table. The method can then be readily implemented in the User class as follows,

use yii\db\ActiveRecord;
use yii\web\IdentityInterface;

class User extends ActiveRecord implements IdentityInterface
{
    public static function findIdentityByAccessToken($token, $type = null)
    {
        return static::findOne(['access_token' => $token]);
    }
}

After authentication is enabled as described above, for every API request, the requested controller will try to authenticate the user in its beforeAction() step.

If authentication succeeds, the controller will perform other checks (such as rate limiting, authorization) and then run the action. The authenticated user identity information can be retrieved via Yii::$app->user->identity.

If authentication fails, a response with HTTP status 401 will be sent back together with other appropriate headers (such as a WWW-Authenticate header for HTTP Basic Auth).

Authorization

After a user is authenticated, you probably want to check if he or she has the permission to perform the requested action for the requested resource. This process is called authorization which is covered in detail in the Authorization section.

If your controllers extend from yii\rest\ActiveController, you may override the checkAccess() method to perform authorization check. The method will be called by the built-in actions provided by yii\rest\ActiveController.