mypmpro-restrict-login-members-only.php

<?php
/**
 * This recipe will prevent members from being able to login unless they have an active membership on your website.
 * 
 * You can add this recipe to your site by creating a custom plugin
 * or using the Code Snippets plugin available for free in the WordPress repository.
 * Read this companion article for step-by-step directions on either method.
 * https://www.paidmembershipspro.com/create-a-plugin-for-pmpro-customizations/
 */
 
function mypmpro_validate_membership_login( $user, $username, $password ){
	
	if( !function_exists( 'pmpro_getMembershipLevelsForUser' ) ){		
		return $user;
	}
	

    	$user = get_user_by( 'login', $username ); 
	
	if( empty( $user ) ) {
	   return;
	}

	if( in_array( 'administrator', $user->roles ) ){
		return $user;
	}

	$membership_levels = pmpro_getMembershipLevelsForUser( $user->ID );

	if( empty( $membership_levels ) ){ //No membership level assigned - no login allowed
	return;
	}

	return $user;

}
add_filter( 'authenticate', 'mypmpro_validate_membership_login', 99, 3 );

For more information about this code recipe, please read the full article here: https://www.paidmembershipspro.com/restrict-user-login-for-members-only/

This recipe is included in the blog post on "Restrict User Login for Members Only" at Paid Memberships Pro here: https://www.paidmembershipspro.com/restrict-user-login-for-members-only/