There are two possible directives for X-Frame-Options:

X-Frame-Options: DENY
X-Frame-Options: SAMEORIGIN

If you specify DENY, not only will the browser attempt to load the page in a frame fail when loaded from other sites, attempts to do so will fail when loaded from the same site. On the other hand, if you specify SAMEORIGIN, you can still use the page in a frame as long as the site including it in a frame is the same as the one serving the page.

DENY

The page cannot be displayed in a frame, regardless of the site attempting to do so.

SAMEORIGIN

The page can only be displayed if all ancestor frames are same origin to the page itself.

ALLOW-FROM=url Deprecated

This is an obsolete directive that no longer works in modern browsers. (Using it will give the same behavior as omitting the header.) Don't use it. The Content-Security-Policy HTTP header has a frame-ancestors directive which you can use instead.

To configure Apache to send the X-Frame-Options header for all pages, add this to your site's configuration:

Header always set X-Frame-Options "SAMEORIGIN"

To configure Apache to set the X-Frame-Options DENY, add this to your site's configuration:

Header set X-Frame-Options "DENY"

To configure Nginx to send the X-Frame-Options header, add this either to your http, server or location configuration:

add_header X-Frame-Options SAMEORIGIN always;

To configure IIS to send the X-Frame-Options header, add this to your site's Web.config file:

<system.webServer>
  …

  <httpProtocol>
    <customHeaders>
      <add name="X-Frame-Options" value="SAMEORIGIN" />
    </customHeaders>
  </httpProtocol>

  …
</system.webServer>

Or see this Microsoft support article on setting this configuration using the IIS Manager user interface.

To configure HAProxy to send the X-Frame-Options header, add this to your front-end, listen, or backend configuration:

rspadd X-Frame-Options:\ SAMEORIGIN

Alternatively, in newer versions:

http-response set-header X-Frame-Options SAMEORIGIN

To configure Express to send the X-Frame-Options header, you can use helmet which uses frameguard to set the header. Add this to your server configuration:

const helmet = require('helmet');
const app = express();
app.use(helmet.frameguard({ action: 'SAMEORIGIN' }));

Alternatively, you can use frameguard directly:

const frameguard = require('frameguard')
app.use(frameguard({ action: 'SAMEORIGIN' }))

• Content-Security-Policy directive frame-ancestors
• ClickJacking Defenses - IEBlog
• Combating ClickJacking with X-Frame-Options - IEInternals