PHP Api Proxy for Laravel 4

Summary

• Introduction
• Installation
• Setup
• Configuration
• Usage
  • Facade
• License

Introduction

This package would be a solution about the issue opened by Alex Bilbie. He says:

Let's assume that you've just made a shiny Angular/Ember/Backbone whatever single page web-app that gets all of it's data from an API that you've written via ajax calls. You've also elected to secure the API with OAuth and you're also securing the API endpoint with SSL (as the OAuth spec requires).

POST /auth HTTP/1.1
Host: api.example.com

grant_type=password
&client_id=webapp
&client_secret=abc123
&username=admin
&password=mypassword

The server will respond:

{
    "access_token": "DDSHs55zpG51Mtxnt6H8vwn5fVJ230dF",
    "refresh_token": "24QmIt2aV1ubaenB2D6G0se5pFRk4W05",
    "token_type": "Bearer",
    "expires": 1415741799
}

Already there are major problems with this.

First in the app's request we're sending the client ID and secret which the API uses to ensure the request is coming from a known source. As there is no backend to the web-app these will have to be stored in the front-end code and they can't be encrypted in code because you can't do crypto in JavaScript securely. So already we've got the problem that the only way of identifying the web-app - by using credentials - are already leaked in public code and will allow an attacker to attempt to make authenticated requests independent of the app. You can't use referrer headers to lock down requests either as they are easily faked. You can't store the credentials in an encrypted form in a cookie either because that cookie can be just grabbed by the attacker as easily as the client credentials that are baked into source code.

Moving on, in the response to the request the server has given us an access token which is used to authenticate requests to the API and a refresh token which is used to acquire a new access token when it expires.

First we've got the issue that the access token is now available to the attacker. He doesn't need anything else now to make requests to your API and go crazy grabbing all of the users' private data and performing any actions that the API allows. The server has got no way of knowing that it isn't the web-app making the requests.

So because this is an app that you've written and it's talking to your backend you've decided that the resource owner password credentials grant (aka the password grant) is the way that you're going to get an access token. The access token can then be used to authenticate API requests.

The web-app is going to make an ajax request to the API to sign the user in once you've captured their credentials (line breaks added for readability). This is how a valid OAuth 2 password grant access token request should look:

Valid request from the web-app:

GET /resource/123 HTTP/1.1
Authorization: Bearer DDSHs55zpG51Mtxnt6H8vwn5fVJ230dF
Host: api.example.com

Valid request from an attacker:

GET /resource/123 HTTP/1.1
Authorization: Bearer DDSHs55zpG51Mtxnt6H8vwn5fVJ230dF
Host: api.example.com

Even if your API has short lived access tokens then the refresh token was also in the response to the browser so the attacker can use that to get a new access token when the original expires.

The simple story is here that you can't keep things safe in the front end. So don't.

So how can you use OAuth securely in single page web-apps?

It's simple; proxy all of your API calls via a thin server side component. This component (let's just call it a proxy from here on) will authenticate ajax requests from the user's session. The access and refresh tokens can be stored in an encrypted form in a cookie which only the proxy can decrypt. The application client credentials will also be hardcoded into the proxy so they're not publicly accessible either.

To authenticate the user in the first place the web-app will make a request to the proxy with just the user's credentials and client ID, NOT CLIENT SECRET!:

POST /ajax/auth HTTP/1.1
Host: example.com

grant_type=password
&username=admin
&password=mypassword
&client_id=webapp

The proxy will then add in the client secret which only it knows and forward the request onto the API:

POST /auth HTTP/1.1
Host: api.example.com

grant_type=password
&username=admin
&password=mypassword
&client_id=webapp
&client_secret=abc123

The server will respond:

{
    "access_token": "DDSHs55zpG51Mtxnt6H8vwn5fVJ230dF",
    "refresh_token": "24QmIt2aV1ubaenB2D6G0se5pFRk4W05",
    "token_type": "Bearer",
    "expires": 1415741799
}

The proxy will encrypt the tokens in a cookie and return a success message to the user.

When the web-app makes a request to an API endpoint it will call the proxy instead of the API:

GET /ajax/resource/123 HTTP/1.1
Cookie: <encrypted cookie with tokens>
Host: example.com

The proxy will decrypt the cookie, add the Authorization header to the request and forward it on to the API:

GET /resource/123 HTTP/1.1
Authorization: Bearer DDSHs55zpG51Mtxnt6H8vwn5fVJ230dF
Host: api.example.com

The proxy will pass the response straight back to the browser.

With this setup there are no publicly visible or plain text client credentials or tokens which means that attackers won't be make faked requests to the API. Also because the browser is no longer communicating with the API directly you can remove it from the public Internet and lock down the firewall rules so that only requests coming from the web server directly will be allowed.

To protect an attacker just stealing the cookie you can use CSRF protection measures.

Thank you to Alex Bilbie for issue: http://alexbilbie.com/2014/11/oauth-and-javascript

Installation

Add the following line to the require section of composer.json:

{
    "require": {
        "thinkingmik/api-proxy-laravel": "1.x"
    }
}

Setup

1. Add 'ThinKingMik\ApiProxy\ApiProxyServiceProvider', to the service provider list in app/config/app.php.
2. Add 'Proxify' => 'ThinKingMik\ApiProxy\Facades\ApiProxyFacade', to the list of aliases in app/config/app.php.

Configuration

In order to use the Api Proxy publish its configuration first

php artisan config:publish thinkingmik/api-proxy-laravel

Afterwards edit the file app/config/packages/thinkingmik/api-proxy-laravel/proxy.php to suit your needs.

Usage

In the app/config/routes.php add a new endpoint like:

Route::match(array('GET', 'POST'), '/proxify', function()
{
	return Proxify::makeRequest(Request::method(), Input::all());
});

This is your proxy endpoint, then you can call proxy to get an access token (the client_id parameter is optional):

POST public/proxify HTTP/1.1
Host: example.com

uri=http://example.com/public/oauth/access_token
&grant_type=password
[&client_id=webapp]
&username=admin
&password=mypassword

And after you can call the protected resource:

POST public/proxify HTTP/1.1
Host: example.com

uri=http://example.com/public/protected_resource

If the access_token expires and you have got a refresh_token, ApiProxy will call the OAuth server for you and refresh the access_token with a new one. After that it makes a new call to the protected resource.

This ApiProxy package works great with oauth2-server-laravel written by Luca Degasperi. I have used this package for my tests.

Facade

The ApiProxy is available through the Facade Proxify or through the proxy service in the IOC container. The method available is:

/**
 * Use this method in the laravel route file
 * @param $method 
 * @param array $inputs
 * @return Response
 * @throws ProxyMissingParamException
 */
Proxify::makeRequest(Request::method(), Input::all());

License

This package is released under the MIT License.