The challenge header names what to send next.
WWW-Authenticate names the challenge
The response row displays the challenge safely as Basic realm toy.
challenge header checked
The exact response bytes are pinned
The trust boundary checks the quoted realm in the pinned response bytes before rendering.
response bytes checked
The challenge has a scheme and a realm
Chapter two reads those two pieces separately.
scheme and realm
Summary
The challenge header tells the client which auth style to try next.
challenge header parsed