function wp_populate_basic_auth_from_authorization_header() {
	// If we don't have anything to pull from, return early.
	if ( ! isset( $_SERVER['HTTP_AUTHORIZATION'] ) && ! isset( $_SERVER['REDIRECT_HTTP_AUTHORIZATION'] ) ) {
		return;
	}

	// If either PHP_AUTH key is already set, do nothing.
	if ( isset( $_SERVER['PHP_AUTH_USER'] ) || isset( $_SERVER['PHP_AUTH_PW'] ) ) {
		return;
	}

	// From our prior conditional, one of these must be set.
	$header = isset( $_SERVER['HTTP_AUTHORIZATION'] ) ? $_SERVER['HTTP_AUTHORIZATION'] : $_SERVER['REDIRECT_HTTP_AUTHORIZATION'];

	// Test to make sure the pattern matches expected.
	if ( ! preg_match( '%^Basic [a-z\d/+]*={0,2}$%i', $header ) ) {
		return;
	}

	// Removing `Basic ` the token would start six characters in.
	$token    = substr( $header, 6 );
	$userpass = base64_decode( $token );

	list( $user, $pass ) = explode( ':', $userpass );

	// Now shove them in the proper keys where we're expecting later on.
	$_SERVER['PHP_AUTH_USER'] = $user;
	$_SERVER['PHP_AUTH_PW']   = $pass;
}