wp_generate_auth_cookie

if ( ! function_exists( 'wp_generate_auth_cookie' ) ) :
	/**
	 * Generates authentication cookie contents.
	 *
	 * @since 2.5.0
	 * @since 4.0.0 The `$token` parameter was added.
	 *
	 * @param int    $user_id    User ID.
	 * @param int    $expiration The time the cookie expires as a UNIX timestamp.
	 * @param string $scheme     Optional. The cookie scheme to use: 'auth', 'secure_auth', or 'logged_in'.
	 *                           Default 'auth'.
	 * @param string $token      User's session token to use for this cookie.
	 * @return string Authentication cookie contents. Empty string if user does not exist.
	 */
	function wp_generate_auth_cookie( $user_id, $expiration, $scheme = 'auth', $token = '' ) {
		$user = get_userdata( $user_id );
		if ( ! $user ) {
			return '';
		}

		if ( ! $token ) {
			$manager = WP_Session_Tokens::get_instance( $user_id );
			$token   = $manager->create( $expiration );
		}

		$pass_frag = substr( $user->user_pass, 8, 4 );

		$key = wp_hash( $user->user_login . '|' . $pass_frag . '|' . $expiration . '|' . $token, $scheme );

		// If ext/hash is not present, compat.php's hash_hmac() does not support sha256.
		$algo = function_exists( 'hash' ) ? 'sha256' : 'sha1';
		$hash = hash_hmac( $algo, $user->user_login . '|' . $expiration . '|' . $token, $key );

		$cookie = $user->user_login . '|' . $expiration . '|' . $token . '|' . $hash;