I trigger the request with this form
<form method="post" action="/sign-in">
<p>
<input type="text" name="username" />
</p>
<p>
<input type="password" name="password" />
</p>
<p>
<button>Sign in</button>
</p>
</form>
The only request part I get is:
head(HTTPRequestHead {
method: POST,
uri: "/sign-in", version: HTTP/1.1,
headers: [("Host", "localhost:8000"), ("Connection", "keep-alive"), ("Content-Length", "31"), ("Cache-Control", "max-age=0"), ("Origin", "http://localhost:8000"), ("Upgrade-Insecure-Requests", "1"), ("Content-Type", "application/x-www-form-urlencoded"), ("User-Agent", "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_4) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/66.0.3359.181 Safari/537.36"), ("Accept", "text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8"), ("Referer", "http://localhost:8000/sign-in"), ("Accept-Encoding", "gzip, deflate, br"), ("Accept-Language", "en-US,en;q=0.9,el;q=0.8")]
})