First of all, if you still don’t know anything about Zend Expressive check it out: http://zendframework.github.io/zend-expressive/

Prerequisites:

• A decent grasp of PHP
• REST fundamentals
• Basic Zend Expressive knowledge

“Token based authentication works by ensuring that each request to a server is accompanied by a signed token which the server verifies for authenticity and only then responds to the request.”

So, we assume that we have a login page that will send the user credentials to our API endpoint (that will be http://api.mvlabs.it/api/v1/user/login in our example) and, if the given credentials are correct, then the API will respond with a token to the Front-End and the Front-End application will use the token to access the restricted resources in the following requests.

OK, so …how can I do that with Zend Expressive?

In Zend Expressive we could use a Middleware plugged into our pipeline to verify the token validity. So, for this scope we’ll use the tuupola/slim-jwt-auth middleware. It was originally developed for Slim but can be used with any framework that complies with the PSR-7 standard and of course, Zend Expressive is one of them! Yep, code reuse is a great thing enabled by Middleware! Ok, let’s take a look. First of all, we need to add to our Zend Expressive skeleton application the jwt auth middleware:

$ composer require tuupola/slim-jwt-auth

Now we need to add some configurations parameters that will be used by the JwtAuthentication Middleware. In fact, the only mandatory parameter is “secret” which is used to verify the token signature, only the issuer application has to know it and should never be disclosed in any way. So:

config/autoload/jwt-authentication.global.php

return [
   'jwt-authentication' => [
       "secret" => getenv("JWT_SECRET"),
       "path" => ["/"],
       "passthrough" => ["/api/v1/user/login", "/api/v1/ping"],
       "error" => function ($request, $response, &$arguments) {
           $data["status"] = "error";
           $data["message"] = $arguments["message"];

           return $response
               ->withHeader("Content-Type", "application/json")
               ->write(json_encode($data, JSON_UNESCAPED_SLASHES | JSON_PRETTY_PRINT));
       }
   ]
];

Some notes about the configuration above:

• The optional path parameter allows us to specify the protected part of your website.
• With optional passthrough parameter we can make exceptions to path parameter.
• error is called when authentication fails. It receives last error message as argument.

Now we can create our JwtAuthentication Middleware through a factory with our configuration defined above.

src/App/Factory/JwtAuthenticationFactory.php

namespace App\Factory;

use Interop\Container\ContainerInterface;
use Slim\Middleware\JwtAuthentication;

class JwtAuthenticationFactory
{
   public function __invoke(ContainerInterface $container)
   {
       $config = $container->get('config');
       return new JwtAuthentication($config['jwt-authentication']);
   }
}

Now is time to add the Jwt Authentication Middleware to the ZE middleware pipeline, then it will have the responsibility to determine if a token is valid for the protected endpoints.

config/autoload/middleware-pipeline.global.php

return [
   'dependencies' => [
       'factories' => [
	...
           Slim\Middleware\JwtAuthentication::class => App\Factory\JwtAuthenticationFactory::class,
	...
       ],
   ],
   'middleware_pipeline' => [
       'always' => [
           'middleware' => [
	       ...
               Slim\Middleware\JwtAuthentication::class,
               ...
           ],
           'priority' => 10000,
    ],
    'routing' => [
       'middleware' => [
            ...
       ],
       'priority' => 1,
    ],
       ...
   ],
];

At this point we need to define some routes in our configuration file, so let’s add the following:

• /api/v1/ping unprotected example endpoint
• /api/v1/user/login (unprotected) used for authentication and token generation
• /api/v1/user/:id the protected endpoint example that returns user specific data

config/autoload/routes.global.php

return [
   'dependencies' => [
       'factories' => [
           App\Action\AuthAction::class => App\Action\AuthFactory::class,
       ],
   ],

   'routes' => [
       [
           'name' => 'api.ping',
           'path' => '/api/v1/ping',
           'middleware' => App\Action\PingAction::class,
           'allowed_methods' => ['GET'],
       ],
       [
           'name' => 'api.auth',
           'path' => '/api/v1/user/login',
           'middleware' => App\Action\AuthAction::class,
           'allowed_methods' => ['POST'],
       ],
       [
           'name' => 'api.user.get',
           'path' => '/api/v1/user/:id',
           'middleware' => App\Action\UsersAction::class,
           'allowed_methods' => ['GET'],
       ],
   ],
];

Now, we need to add the logic that will handles the data sent by the login form, validate it against a database, and after determining that the credentials are valid, will generate the token. So, we’ll define the AuthAction Middleware that will have those responsibilities:

namespace App\Action;
namespace App\Action;

use App\Entity\User;
use App\Service\UserService;
use Psr\Http\Message\ResponseInterface;
use Psr\Http\Message\ServerRequestInterface;
use Zend\Diactoros\Response\JsonResponse;

class AuthAction
{
    private $userService;

    public function __construct(UserService $userService)
    {
        $this->userService = $userService;
    }

    public function __invoke(ServerRequestInterface $request, ResponseInterface $response, callable $next = null)
    {
        $post = $request->getParsedBody();
        $username = $post['username'];
        $password = $post['password'];

        $user = $this->userService->getUserByEmailPassword($username, $password);
        if ($user instanceof User) {
            $jwt = $this->userService->getAuthTokenForUser($user);

            return new JsonResponse([
                'time' => time(),
                'jwt' => $jwt,
            ]);
        }

        return new JsonResponse(['status' => 'error'], 401);
    }
}

Let’s take a detailed look to the token generation in the UserService:

namespace App\Service;

use App\Entity\User;
use Firebase\JWT\JWT;

class UserService
{

    ...

    public function geAuthTokenForUser(User $user)
    {
        $now = new \DateTime();
        $future = new \DateTime("now +2 hours");

        $random_number = openssl_random_pseudo_bytes(32); //generate using openssl_random_pseudo_bytes
        $jti = hash('sha256', $user->getId() . $random_number);
        $serverName =  $this->config['api']['endpoint'];
        /*
         * Create the token as an array
         */
        $data = [
            "iat" => $now->getTimeStamp(),  // Issued at: time when the token was generated
            'jti' => $jti, // Json Token Id: an unique identifier for the token
            'iss' => $serverName, // Issuer
            'nbf' => $now->getTimeStamp()+10, // Not before
            "exp" => $future->getTimeStamp(), // Expire
            'data' => [ // Data related to the signer user
                'userId' => $user->getId(), // userid from the users table
                'username' => $user->getUsername(), // User name
            ]
        ];

        /*
         * Encode the array to a JWT string. Second parameter is the key to encode the token.             *
         * The output token $jwt can be validated at http://jwt.io/
         */
        $jwt = JWT::encode(
            $data,
            $this->config['jwt-authentication']['secret'],
            "HS512"
        );

        return $jwt;
    }
}

In order to check that everything is OK, let’s do a test call to our authentication endpoint with postman, passing our authentication credentials.

Good, everything looks fine, so, at this point the client will have the token, and can store it using a storage mechanism like HTML5 Web Storage.

Now let’s retrieve a resource that is protected by our JWT mechanism. But first we need to set the Authorization header with the contents of the JWT in the format of Bearer [JWT]

As we can see in the image above, we can access to the restricted resource once that we passed our authentication token.

Summary

This is a very reliable method to secure your information. From here on, you can try to implement a token based authentication using ZE in your next API. Feel free to share your constructive feedback or ask a question. Drop a note below, we’ll be happy to receive your comments!

PSR-7

It all started with PSR-7, a set of common interfaces for representing HTTP messages in PHP, allowing application abstraction from the HTTP layer.

The most important aspect of PSR-7 is that it is framework independent and hence its interfaces can easily be used with multiple frameworks such as Symfony, Zend Framework, Laravel or any other framework.

This capability allows developers to write framework agnostic code with a wider opportunity to be reused in other projects, relying on the PSR-7 interfaces only.

PHP AND MIDDLEWARE

The other important key-word is middleware: once the PHP ecosystem gained a nice abstraction over HTTP messages, it was time to think about the best way to write web applications on top of this abstraction.

Citing Matthew Weier O’Phinney, the concept of middleware can be summarized in a single method signature:

function (request, response) : response

The idea is that objects representing the HTTP request and the HTTP response are passed to a callable, which does something with them to return an HTTP response.

This turns out to be a very easy and composable pattern, which had actually already been used with great success in several other programming languages.

The standard way to compose such middleware is to pass a third argument to the callable, so to allow for another layer of middleware to be invoked:

function (request, response, next) : response
{
    // do something on request

    response = next(request, response)

    // do something on response

    return response
}

Several frameworks, as Zend Expressive, Slim, Radar or Spiral rely nowadays upon the concept of middleware to create web applications.

MIDDLEWARE REUSE

Now that we have a highly composable pattern based upon a framework agnostic HTTP abstraction, we can actually start writing highly reusable components that would work on any PHP project. This definitely helps developers easing their daily job.

We can have middleware taking  care of logging all received requests, middleware to perform routing, middleware to manage authentication and some other to take care of user sessions. We use our framework to simply glue all this pieces together in the appropriate way.

The key question at this point should be: has anybody else already implemented the piece of middleware I need for the application I’m developing?

PHP-MIDDLEWORLD IS HERE!

Until now the answer to the previous question could only be gathered through Packagist, Github, or – in the worst case – google.

Having received so much from the community over the years, we thought it was about time to give something back. That’s how php-middleworld.com was born. With the aim to provide fellow PHP developers a means to quickly locate the middleware they need (often with multiple implementation choices).

THE FUTURE

We already have in mind several improvements for php-middleworld.com.

First of all we would like to enable fellow developers to add their own middleware, so that our database could grow with a shared effort.

Then we would also like to add PSR-15 compatible middleware support also, so to be ready when that proposal will be approved.

No need to get any deeper here, to find out more just head to php-middleworld.com and follow @phpmwd on Twitter!

Stay tuned!

The problem

Let’s say you are also developing a PHP application and you want to use docker in your development machine. You will notice that – if you use the official PHP images from the docker hub – sending e-mail out of the box simply won’t work. Lets’ see what I mean in practice, considering this simple index.php file, sending out an e-mail:

$result = mail("info@example.com", "Subject", "The very important email body");

if ($result) {
    echo "Email sent correctly";
} else {
    echo "Error sending the email";
}

Please note: using the mail command to send an email is the simplest way, but there are many more powerful libraries out there that could make things easier. We have chosen to use the mail command just to keep the example as simple as possible.

If we run it using docker with the following command:

docker run -p "80:80" -v `pwd`:/var/www/html --rm php:7-apache

and visit http://localhost with our browser, we’ll see that the mail command will fail, and we’ll get an “Error sending the email” message.

The reason why this happens is that the “mail” command relies on the “sendmail” system command inside the container, which is missing from the official PHP docker image.

While you could simply create a new image extending the original one and adding the sendmail command, I suggest using a different strategy.

Here at MV Labs we do use a tool called Mailhog (https://github.com/mailhog/MailHog) which acts as an SMTP server listening on port 1025 but instead of sending real emails to your recipients, it simply displays them in a handy web interface (which is listening, by default, on port 8025). This way you avoid the risk of sending your testing e-mails to the customer (it happened at least once to everybody) and you don’t have to deal with spam filters or other annoyances in the e-mail chain.

So, how can we achieve this? To make things easier, we can take advantage of docker-compose. Let’s start by adding the mailhog container to our services:

version: '2'
services:
  php:
    image: php:7-apache
    volumes:
      - .:/var/www/html/
    ports:
      - 80:80
    networks:
      - base
  mailhog:
    image: mailhog/mailhog
    ports:
      - 8025:8025
    networks:
      - base
networks:
  base:

Now, if we run docker-compose up and head our browsers to http://localhost:8025 we should see the mailhog simple but powerful web interface.

We’re not done yet, though, as we still need to tell the mail command to send emails through our new mailhog smtp server. Unluckily this requires the building of a custom docker image, since PHP doesn’t allow using the native mail command to connect to a SMTP server. For this reason, we need a tool called ssmtp (https://linux.die.net/man/8/ssmtp) which is basically a configurable sendmail command replacement, and which forwards the message to a SMTP server configured in its config file. We’ll need the following Dockerfile:

FROM php:7-apache

# install ssmtp
RUN apt-get update; apt-get install ssmtp -y

# tell php to use ssmtp's sendmail for email sending
RUN echo "sendmail_path=/usr/sbin/sendmail -t -i" >/usr/local/etc/php/conf.d/sendmail.ini

# tell ssmtp to use mailhog as the mail transport
RUN echo "Mailhub=mailhog:1025" > /etc/ssmtp/ssmtp.conf
RUN echo "FromLineOverride=Yes" >> /etc/ssmtp/ssmtp.conf

Then we’ll need to tell docker-compose.yml to build the image from the Dockerfile for our PHP container:

version: '2'
services:
  php:
    build: .
    volumes:
      - .:/var/www/html/
    ports:
      - 80:80
    networks:
      - base
  mailhog:
    image: mailhog/mailhog
    ports:
      - 8025:8025
    networks:
      - base
networks:
  base:

and build our containers again with:

docker-compose up -d --build

Now we’re ready to send our first “virtual” email. Just head your browser to http://localhost and you’ll get the message “Email sent correctly”. If you check your mailhog at http://localhost:8025 you’ll see your email!

Summary

Using a simple example, we have demonstrated one possible solution for sending test e-mails out of our web applications under development in a secure and handy way, by using some nice open source tools such as SSmtp and Mailhog inside a docker dev environment.

Let us know what you think in the comments area below and happy developing!

The problem: where assets should be placed?

The first problem to solve is: where my module’s assets should be placed to let me (the developer) forget about them? Because I should not care about assets provisioning, I would spend my time working on module itself! To simplify the problem, let me break it into two (not so) different use cases.

Shared assets

A module probably has many shared assets with other modules: javascript libraries, images, css files, etc. A common practice is to place all of them inside the project /public folder. Despite this is the simplest solution, it’s not the best. Copy/paste manually is never a good practice, besides copying all files inside the same folder will contribute to lose the explicit dependencies the module has with its assets.

Single module’s assets

In many cases a module has also some assets being used only by itself. We know that a module should focus on a single project functionality, so it should contain all the things that functionality needs to work well. The simplest answer now is probably the best: we should place all assets inside the module.

Some naive solutions

How should we make the web server aware that out modules have some assets that need to be visible inside our view scripts?

We could copy all assets (also those needed by a single module) inside public folder, every time one of them is added or updated. This is a bad practice, trust me!

We could use symlinks to let files be viewed inside another folder. Or we could do some apache htaccess tuning to let web server search files through all module folders. Luckily, there is a better way to handle things…

Welcome AssetManager module

AssetManager is a ZF2 module (https://github.com/RWOverdijk/AssetManager) aimed at managing assets, that resolve exactly our problem. It’s based on the Assetic asset management framework for PHP (https://github.com/kriswallsmith/assetic).

I don’t cover module provisioning and installation phases here because online there are straightforward and well organized articles about this (take a look on module’s wiki: https://github.com/RWOverdijk/AssetManager/wiki).

Instead, here I would like to explain how this module can be a real time (and headache) saver for all ZF2 developers.

After completing the install process, the module can take care of your assets through two simple steps:

1. Create a folder where assets should be placed. I typically suggest to use the /assets folder inside your module. Obviously you’re free to use whatever name you prefer. Sometimes you find assets inside a folder named /public, but this could be confused with the folder where the web server points to. So I suggest to choose a different name to make things clear. Use the folder you prefer, but keep in mind the rule of thumb: use always the same location inside all your modules, to make them more clear and readable.
2. Add the following rule to your module’s configuration file (/config/module.config.php – “assets” refers to the folder where your assets are placed):

'asset_manager' => array(
    'resolver_configs' => array(
        'paths' => array(
            __DIR__ . '/../assets',
        ),
    ),
),

With this two simple steps we are telling the AssetManager where the assets of our module are placed.

That’s it! Now when an asset is not found inside project /public folder, the AssetManager module’ll look inside our module /assets folder to find the requested file. From now you could link assets inside your views simply as follows:

<?php  echo $this->headLink()->prependStylesheet($this->basePath() . 
                                                '/css/aCssFile.css'); ?>

In this way, we don’t need to worry about where our css is physically located, just link it as if it was placed inside /public folder. So simple and so amazing! In this way you can place all module assets (both shared and exclusive) inside the module. So that module is now really reusable inside other projects, without hidden dependencies.

Pay only attention to avoid colliding file rules. It’s not uncommon to have modules containing files with the same name. In this case prefixing the asset path with the module’s name (or slug) could solve the issue (this can be done through the ‘map’ key inside configuration file; take a look on the code in the following paragraphs for an example).

This is the simplest use of AssetManager we could make, but this module has many more features that are worth an extra look. Let me define some terms the module uses (each of this maps to a key of module’s config file):

• Resolvers (resolver_configs key) allow to define where assets should be searched and how they are named / arranged. Many resolver types are available: MapResolver, CollectionResolver, PrioritizedPathsResolver and PathStackResolver (detailed infos and examples available here: https://github.com/RWOverdijk/AssetManager/wiki/Resolvers)
• Filters (filters key) allow make some processing on assets before serving them (eg. Minify minification, compiling of css files)
• Cache (caching key), as the name suggest, allows to choose which caching policy use to speed up assets serving time

An example

It’s a common practice to merge css files in order to limit the number of http requests (improving page serving speed). The AssetModule could help us to merge files automatically. Supposing our module has two css files (main.css and custom1.css), we could merge them together simply updating module’s config file as follows:

'asset_manager' => array(
    'resolver_configs' => array(
        'map' => array(
            'css/main.css' => __DIR__ . '/../assets/css/main.css',
            'css/custom1.css' => __DIR__ . '/../assets/css/custom1.css',
        ),
        'collections' => array(
            'css/merge.css' => array(
                'css/main.css',
                'css/custom1.css',
            ),
        ),
    ),
),

And the resulting view script is:

<?php echo $this->headLink()->prependStylesheet($this->basePath() . 
                                                '/css/merge.css'); ?>

More code samples can be found on official module wiki (https://github.com/RWOverdijk/AssetManager/wiki), that’s really well written and full of useful examples.

Conclusion

There are other ZF2 modules that provide asset management features. I personally like AssetManager because it’s really effective and simple to use. However is not important which module you decide to use, the important thing is that you should stop right now to manage assets manually. It’s a real boring and time wasting task, especially in the long run.

So now you’ve no excuses, this module requires no more than a few minutes to be installed and configured. Go and give it a try! And… after having configured your assets, don’t forget to enable AssetModule’s cache. That’s really a must to offer decent website performance and hence a good user experience.

For those who prefer a talk-like explanation, the extract of my Zend Framework Day presentation about this topic can be found here.

Image credit: http://www.flickr.com/photos/tracyleephoto/8322509672

The Problem

Script wasn’t outputting nor logging anything, so in order to find out more about the problem, I thought about logging last script execution datetime myself. I wanted to find out whether the problem was related to cron execution, or rather to some issue within the script itself. So I added following two lines (on top to the script):

$s_content = 'Script last run: '. date("d/m/Y h:i:s" . "\n");
file_put_contents('/tmp/cert_import.log', $s_content);

And executed it:

php ./importa_certificati.php

All I got was a nasty error message:

File size limit exceeded

At first I thought the problem might’ve been related to the specific file name I had picked (IE /tmp/cert_import.log). Did it exist already and was it already too big? I was sure I had checked things out. And actually, file wasn’t there upon a second check. So what was PHP ranting about? Could have it been a permission issue? Nope, script was being executed by root and was executable. So, where did the problem lie? I started to search for the problem by reverting the script to its original form, commenting out my additions:

// $s_content = 'Script last run: '. date("d/m/Y h:i:s" . "\n");
// file_put_contents('/tmp/cert_import.log', $s_content);

Problem magically disappeared. Weird, I thought. “Let’s see what happens if I prepare my string, but don’t it write to the file, I said to myself. I’m sure the problem lies there. Let’s check”:

$s_content = 'Script last run: '. date("d/m/Y h:i:s" . "\n");
// file_put_contents('/tmp/cert_import.log', $s_content);

File size limit exceeded

Whaat?!? Problem still there, despite no attempt to write to a file is even made. Things start to look awkward.

The Cause

What I had just discovered was that problem didn’t have anything to do with the file I was trying to write, but was related instead to the PHP process itself. In fact, wondering what other file size limit might’ve been reached, I came to think about logging. So, I opened php.ini and checked things out. Logging was configured indeed, pointing at /usr/local/zend/var/log/php.log through following directives:

; http://php.net/log-errors
log_errors = On

; Set maximum length of log_errors. [...]
log_errors_max_len = 1024

; Log errors to specified file. PHPs default behavior is to leave this value
; empty.
error_log = "/usr/local/zend/var/log/php.log"

I changed my working directory to /usr/local/zend/var/log/ and checked things out with ls:

[root@XXX ~]# cd /usr/local/zend/var/log/
[root@XXX log]# ls -alh
-rw-rw---- 1 apache zend 2.0G Dec 27 17:30 php.log

That exact 2Gb size looked suspicious, to say the least. Especially because the php.ini log_errors_max_len directive above had a 1024 value, not a 2048 one. So, I moved the log file out of its way, and gzipped it (so to save some space, without losing anything).

mv php.log
gzip php.log

I then run the script again. All went well this time, with no error being reported. Problem was caused by log file size indeed. Most likely no one cared about rotating it, believing that log_errors_max_len would do the job. As it’s explained on stackoverflow though, despite its possibly ambiguous name, log_errors_max_len only deals with the size of a single log message, not with the size of the log file itself.

Newly introduced problem was solved. But I was still wondering what might’ve caused the problem from the lines I had added in first place. Luckily I now had logs to check.

The timezone not set and include underlying issues

I opened the new php.log file and found a few entries like the following:

[05-Dec-2012 23:00:04 UTC] PHP Warning:  strtotime(): It is not safe to rely on the system's timezone settings. 
You are *required* to use the date.timezone setting or the date_default_timezone_set() function. 
In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. 
We selected 'Europe/Berlin' for 'CET/1.0/no DST' instead in /[...]/importa_certificati.php on line 14

Easy problem to fix. And also found the reason why log file filled up so quickly. Such message was written for every run of another script where the date function was used.

Still, I hadn’t solved my problem yet. Script would run from console, but wouldn’t from cron. Again, logs proved to be my friends, with entries like the following:

[27-Dec-2012 23:09:02 UTC] PHP Warning:  include_once(../classi/dbconnect.php): failed to open stream: No such file or directory in /[...]/importa_certificati.php on line 3
[27-Dec-2012 23:09:02 UTC] PHP Warning:  include_once(): Failed opening '../classi/dbconnect.php' for inclusion (include_path='.:/[...]') in /[...]/importa_certificati.php on line 3
[27-Dec-2012 23:09:02 UTC] PHP Warning:  include_once(../classi/utils.php): failed to open stream: No such file or directory in /[...]/importa_certificati.php on line 4
[27-Dec-2012 23:09:02 UTC] PHP Warning:  include_once(): Failed opening '../classi/utils.php' for inclusion (include_path='.:[...]') in /[...]/importa_certificati.php on line 4
[27-Dec-2012 23:09:02 UTC] PHP Fatal error:  Class 'utils' not found in /[...]/importa_certificati.php on line 10

I had just found out that problem was due to the script having relative includes in the following form:

<!--?php

include_once('../classes/dbconnect.php');
include_once('../classes/utils.php');

$s_pathCerts = __DIR__ . '/../rsync/data';

</pre-->

So everything worked when the script was tested by customer from local directory:

php ./importa_certificati.php

But once it was invoked by cron, it stopped working, since path wasn’t quite the same.
And, because no error messages related to the issue were collected in php.log, no one ever discovered about the problem with the script, and blamed cron settings instead.
Changing lines above tothe following solved the problem:

<!--?php

include_once(__DIR__ . '/../classes/dbconnect.php');
include_once(__DIR__ . '/../classes/utils.php');

$s_pathCerts = __DIR__ . '/../rsync/data';

</pre-->

Things to take home from this experience

1. If php can not write to its log file it will stop script execution, without giving a clear explanation of what’s going on
2. The log_errors_max_len directive is a bit ambiguous. It deals with each log record, not with the whole file size
3. You always need to set your timezone, if you don’t want to have your logs filled with crap
4. When including stuff, it’s wise to rely on the php __DIR__ or dirname(__FILE__) constructs rather than on relative paths. You can’t be sure the scritpt will be invoked from where you expect.
5. When troubleshooting it’s important to think “outside” the box. In this case the problem was related to the script itself, as much as it was related to its environment.
6. If you do write to logs, you need to check’em out every once in a while. Having their content e-mailed to you periodically is also a good idea

Elephant picture courtesy of http://www.flickr.com/photos/laughingsquid/2218075860/