Is there an event hook function that is called after a request is fully prepared?

Thank you for allowing us to use your wonderful library.

Please let me know if you know of any of the following functions

Is there an event hook function that is called just before sending a request, like the event hooks in python's httpx library? When sending a request, we need to add a signature computed from the header and body of the request packet.
https://www.python-httpx.org/advanced/#event-hooks

I can't rewrite the request in Middleware because the request is not mut.

Start by reviewing the Middleware API and the request-sending path to determine whether a hook runs after the request is fully prepared but before transmission. Check how headers and the body are exposed at that point, and document whether the existing API supports signing or what lifecycle behavior would need to be added.

Written by the indexing model from the issue text.