fetch() and XHR did String(body), so passing a FormData as the request body
sent the literal "[object Object]" and lost the multipart payload along with
its boundary. Servers expecting multipart/form-data replied 400 "Invalid
boundary for multipart/form-data", which is what blocked booking.com: the AWS
WAF challenge POSTs its proof-of-work solution to /mp_verify as FormData, so
the verify always failed and no aws-waf-token was issued. Serialize FormData to
a multipart/form-data body with a generated boundary and set the matching
Content-Type, the way a real browser does; URLSearchParams bodies get
application/x-www-form-urlencoded. XHR.send routes through fetch() so it is
covered too. With this, obscura --stealth renders the real booking.com landing
page the same as headless Chrome.
SGavrl
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