wp-login-filter.php

<?php
  	/**
	 * Filters the link text of the header logo above the login form.
	 *
	 * @since 5.2.0
	 *
	 * @param string $login_header_text The login header logo link text.
	 */
	$login_header_text = apply_filters( 'login_headertext', $login_header_text );