You cannot. Google servers will not accept any
CORS (Cross-Origin Resource Sharing)[
^] request. Allowing that would be a major security issue.
The
iframe
tag is not responsible for this behaviour, there is nothing you can do, server or client-side, to prevent that: it is the target server of the iframe (i.e., google) which explicitly refuses to serve your request.
[Edit]: replace 'google' by what is appropriate in your case :)