Filter and manipulate the get_current_user() function

From what I’m seeing in the github repo.
get_current_user doesn’t exist.
What you do have is wp_get_current_user, this function does this

return _wp_get_current_user();

So now I checked what _wp_get_current_user does.
It checks a global variable $global_user, if it’s not empty, return an instance of it (didn’t find any actions for that).
If empty it does a few checks and runs wp_set_current_user(), this function has one action

 * Fires after the current user is set.
 * @since 2.0.1
do_action( 'set_current_user' );

So you can hook into it and use global $current_user;

_wp_get_current_user also has a filter, also at the end of the function block.

 * Filters the current user.
 * The default filters use this to determine the current user from the
 * request's cookies, if available.
 * Returning a value of false will effectively short-circuit setting
 * the current user.
 * @since 3.9.0
 * @param int|false $user_id User ID if one has been determined, false otherwise.
$user_id = apply_filters( 'determine_current_user', false );

I’m not sure how much help any of those events are but worth a shot.