Manual:$wgApiFrameOptions/de-formal

Details
Disallow framing of API pages directly, by setting the X-Frame-Options header. Since the API returns CSRF tokens, allowing the results to be framed can compromise your user's account security.

Options are:


 * 'DENY' - Do not allow framing. This is recommended for most wikis.
 * 'SAMEORIGIN' - Allow framing by pages on the same domain.
 * false - Allow all framing.