minor #12117 add support for custom headers when using a proxy (brambaud)

This PR was merged into the 3.4 branch.

Discussion
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add support for custom headers when using a proxy

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See symfony/symfony#32961 and symfony/symfony#26333.

We should document how to use custom headers when using reverse proxies since `Request::setTrustedHeaderName()` has been deprecated.

Commits
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a63c5a6 add support for custom headers when using a proxy

Author: OskarStark

deployment/proxies.rst

@@ -76,4 +76,21 @@ That's it! It's critical that you prevent traffic from all non-trusted sources.
 If you allow outside traffic, they could "spoof" their true IP address and
 other information.
 
+Custom Headers When Using a Reverse Proxy
+-----------------------------------------
+
+Some reverse proxies (like CloudFront with ``CloudFront-Forwarded-Proto``) may force you to use a custom header.
+For instance you have ``Custom-Forwarded-Proto`` instead of ``X-Forwarded-Proto``.
+
+In this case, you'll need to set the header ``X-Forwarded-Proto`` with the value of
+``Custom-Forwarded-Proto`` early enough in your application, i.e. before handling the request::
+
+    // web/app.php
+
+    // ...
+    $_SERVER['HEADER_X_FORWARDED_PROTO'] = $_SERVER['HEADER_CUSTOM_FORWARDED_PROTO'];
+    // ...
+    $response = $kernel->handle($request);
+
 .. _`security groups`: http://docs.aws.amazon.com/elasticloadbalancing/latest/classic/elb-security-groups.html
+.. _`RFC 7239`: http://tools.ietf.org/html/rfc7239