For security reasons, Fiddler forbids the Host
header and URL Host
In the default (traffic capture) case, any mismatch results in Fiddler showing a warning before overwriting the Host header with the Host specified by the URL.
In the special case of the Composer, no warning is shown and the value in the Host header is used. At some point, things will probably be changed to make the Composer behave more like the traffic capture codepath.
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