wp-includes/class-wp-http-proxy.php:155Retrieve header string for proxy authentication.
string public function authentication_header() { return 'Proxy-Authorization: Basic ' . base64_encode( $this->authentication() ); }Introduced in 2.8.0. Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-includes/class-wp-http-proxy.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.