Newbie question. Login/Registration. New PHP page

Question

Being a programmer from a completely different background, I have some pretty novice questions about wordpress and PHP that I could not find the answers for on the internet, probably because they are too basic. Sorry if some you find these questions way too silly, but I could not find answers for these on the web. Hence asking

1. I am trying to create a simple login/registration functionality to add to my wordpress site. I could not find a plugin doing that. All I found is plugins helping to customize the admin login page of wordpress (like CustomLogin). Is there one that can help me?

2. I saw some functions named 'signon', and 'isusersignedin' and a table called wp_users in the database. Can these functions be used for my purpose or are they reserved only for the admin login of the wordpress website? I am also unlcear about what is the difference between wp-admin and wp-login. They both allow for the site to be edited byt the admin

3. Trying to implement it on my own in PHP, I seem to be really confused about the PHP structure that wordpress uses. For example, while implementing a registration form, I will need a page that takes the input from the post method and writes a new row to the database table. For that I cannot use the regular template that I am using for all my pages. Do I have to create a new template page for just this one extra thing? Isn't there some way of just calling an extra function somewhere based on some condition

Thanks & Regards Rahul

Answer 1

WordPress Core provides a lot of helper functions to accomplish these types of tasks. If it's not a function, then there most often is a filter or action that you can hook into.

In the case of the WordPress login form, it's wp_login_form(). Here documentation on that: https://codex.wordpress.org/Function_Reference/wp_login_form

Regarding redirecting users after login, there's a filter for that. This code is a snippet I've used on many sites:

function wip_login_redirect( $url, $request, $user ){
 $slug = $_SERVER["REQUEST_URI"];
 $islogin = strpos($slug, 'log-in');

 if( $user && is_object( $user ) && is_a( $user, 'WP_User' ) ) {

 if(($user->has_cap('edit_users')) && ($islogin==true)) {
 $url = admin_url('index.php');
 } elseif ((!$user->has_cap('edit_users')) && ($islogin==true)) { 
 $url = home_url();
 } else {
 $url = $slug;
 }
 }
 return $url;
}

add_filter('login_redirect', 'wip_login_redirect', 10, 3 );

I go into detail about that in this article: https://wordimpress.com/conditional-custom-login-redirects-wordpress/

Hope that gets you going in the right direction.