Symfony Version 3.4, PHP 7, Apache 2.4

What we are trying to do?

We are trying to restrict a route (/anon/foo) to a set of IPs via Symfony's security access_control. The IPs will be read as a runtime environment variable from Apache. To group the IPs together, we will use a json encoded string containing multiple IPs and then have symfony decode them using Symfony's Json environment variable processor.

STEP 1:
Set up an environment variable as a json encoded string in Apache as below:

<VirtualHost *:443>
    ...
    SetEnv whitelisted_ip "[\"127.0.0.1\", \"127.0.0.2\"]
</VirtualHost>

STEP 2:
Set up your application's parameter.yml to decode that environment variable as below:

    whitelisted_ips_for_access_control: '%env(json:whitelisted_ip)%'

Step 3:
Observe the parameter in \Symfony\Component\HttpKernel\Kernel::handle after $this->boot(); The values have been decoded into an array perfectly.

        $this->boot();
        $foo = $this->getContainer()->getParameter( 'whitelisted_ips_for_access_control');

Step 4:
Set security.yml so that the route is only accessibly via certain IPs as below:

security:
...
    firewalls:
        anon_area:
            pattern: ^/anon
            anonymous: true
...
    access_control:
        - { path: ^/anon/foo, roles: IS_AUTHENTICATED_ANONYMOUSLY, ips: '%whitelisted_ips_for_access_control%' }
        - { path: ^/anon/foo, roles: ROLE_NO_ACCESS}

Step 5:
Clear cache and observe the container file var/cache/test/ContainerP59owun/getSecurity_AccessMapService.php. Notice that the variable has been passed to RequestMatcher as an array array(0 => $this->getEnv('json:whitelisted_ip'))

<?php

use Symfony\Component\DependencyInjection\Argument\RewindableGenerator;

// This file has been auto-generated by the Symfony Dependency Injection Component for internal use.
// Returns the private 'security.access_map' shared service.

$this->services['security.access_map'] = $instance = new \Symfony\Component\Security\Http\AccessMap();

$a = new \Symfony\Component\HttpFoundation\RequestMatcher('^/anon/foo');

$instance->add(new \Symfony\Component\HttpFoundation\RequestMatcher('^/anon/foo', NULL, array(), array(0 => $this->getEnv('json:whitelisted_ip'))), array(0 => 'IS_AUTHENTICATED_ANONYMOUSLY'), NULL);

Step 6:
Go back to your application's parameters.yml that you changed in Step 2. Now change that parameter as below:

    whitelisted_ips_for_access_control: ["127.0.01", "127.0.02"]

Step 7:
Clear cache again and observe the same container file Tests/_app/var/cache/test/ContainerAjyqbl9/getSecurity_AccessMapService.php

<?php

use Symfony\Component\DependencyInjection\Argument\RewindableGenerator;

$this->services['security.access_map'] = $instance = new \Symfony\Component\Security\Http\AccessMap();

$a = new \Symfony\Component\HttpFoundation\RequestMatcher('^/anon/foo');

$instance->add(new \Symfony\Component\HttpFoundation\RequestMatcher('^/anon/foo', NULL, array(), $this->parameters['whitelisted_ips_for_access_control']), array(0 => 'IS_AUTHENTICATED_ANONYMOUSLY'), NULL);

Step 8:
Compare the following two lines from Step 7 and Step 5

with parameter set as whitelisted_ips_for_access_control: '%env(json:whitelisted_ip)%'

$instance->add(new \Symfony\Component\HttpFoundation\RequestMatcher('^/anon/foo', NULL, array(), array(0 => $this->getEnv('json:whitelisted_ip'))), array(0 => 'IS_AUTHENTICATED_ANONYMOUSLY'), NULL);

with parameter set as whitelisted_ips_for_access_control: ["127.0.01", "127.0.02"]

$instance->add(new \Symfony\Component\HttpFoundation\RequestMatcher('^/anon/foo', NULL, array(), $this->parameters['whitelisted_ips_for_access_control']), array(0 => 'IS_AUTHENTICATED_ANONYMOUSLY'), NULL);

When the parameter is being read at runtime, a ContextErrorException is thrown at vendor\symfony\symfony\src\Symfony\Component\HttpFoundation\IpUtils.php (line 66) since the run time environment variable was wrapped in an array rather than be passed directly.