How to modify HTTP headers using .htaccess files

Modifying HTTP headers

On Hostvento Hosting servers, the mod_headers module is part of the Apache setup. This means that the Header directive in a.htaccess file can be used to add, edit, and remove HTTP response headers with ease.

When working with headers, debugging becomes considerably simpler with the use of a browser plugin that allows you to view the raw headers (such as Live HTTP headers for Firefox). You can view the raw HTTP headers for requests and responses as they are delivered and received with these kinds of plugins.

Adding a header

To add a custom header to the HTTP response headers, use the set or append option. The set option sets the specified header and replaces any header that has the same name. Alternatively, the append option sets the header if it does not already exist. If the header already exists, however, the append option adds to the existing header value.

For example, the following sample configuration demonstrates how to set a header and append to a header:

<IfModule mod_headers.c>
  Header set Animal cow
  Header set Animal monkey
  Header append Animal camel
</IfModule>

In this example, the Animal header is first set to cow. But because the next header option is also set, the Animal header is reset to monkey. Lastly, camel is appended to the Animal header. This generates an HTTP response header that resembles the following:

HTTP/1.1 200 OK
Date: Tue, 24 Jun 2014 15:23:33 GMT
Server: Apache
Animal: monkey, camel

Editing a header

To edit a header, use the edit option. With the edit option, you can use regular expressions to do search-and-replace operations on header values.

For example, the following sample configuration demonstrates how to do a (very) simple search-and-replace operation on a header:

<IfModule mod_headers.c>
  Header set Animal monkey 
  Header append Animal camel
  Header edit Animal "camel" "llama"
</IfModule>

In this example, camel is replaced by llama. This generates an HTTP response header that resembles the following:

HTTP/1.1 200 OK
Date: Tue, 24 Jun 2014 15:42:21 GMT
Server: Apache
Animal: monkey, llama

The Header edit option runs before any application-generated headers. Therefore, if you are trying to modify a header that is generated by an application (for example, WordPress or Drupal), you should use the Header always edit option instead. This option ensures that Apache modifies the headers after an application generates them.

Removing a header

To completely remove a header from an HTTP response, use the unset option.

The following sample configuration demonstrates how to remove a header:

<IfModule mod_headers.c>
  Header unset Animal
</IfModule>