Mapping Domains to Permalinks (not multisite)

I am trying to do this on a standalone WP installation (not multisite). What I am trying to achieve is:

1. User saves domain.com on usermeta. (done)
2. User creates a new CPT, say company. Which is accessible via by default original.com/company/example-company (done – by default)
3. I need all the posts created by the user to make available also via domain.com/company/example-company when the usermeta domain is set.

I understand that the DNS and domain should be pointed to current WP installation (irrelevant), but not sure how to map the domain to a permalink.

Algorithm Should Be Something Like This

1. Check if company CPT single page is shown.
2. Check if the author set a domain.
3. If domain is set, modify the permalink.

Answers:

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Method 1

If you set domain.com as an alias of original.com, in WordPress you have to do nothing to make it works.

The problem is the countrary: once in DNS the 2 domains are aliases, every url of your WordPress will be accessible via user defined domains: domain.com/any/wp/url, but also domain2.com/any/wp/url, domain3.com/any/wp/url and so on…

So, what you have to do, is

1. Check if the url is one of the user defined domain
2. If so, check if the page requested is a singular CPT and its author
   is the one that saved the domain
3. If not, redirect the request to the original domainù

Let’s assume you save yout original domain in a constant, maybe in wp-config.php

define('ORIGINAL_DOMAIN', 'original.com');

now you can easily implement the workflow described above:

add_action('template_redirect', 'check_request_domain', 1);

function check_request_domain() {
  $domain = filter_input(INPUT_SERVER, 'HTTP_HOST', FILTER_SANITIZE_URL);
  // strip out the 'www.' part if present
  $domain = str_replace( 'www.', '', $domain);

  // if the request is from original domain do nothing
  if ( $domain === ORIGINAL_DOMAIN ) return;

  // if it is not a singular company CPT request redirect to same request
  // but on original domain
  if ( ! is_singular('company') ) {
    redirect_to_original(); // function defined below
  }

  // if we are here the request is from an user domain and for a singular company request
  // let's check if the author of the post has user meta, assuming meta key is `'domain'`
  // and the meta value is the same of domain in current url

  $meta = get_user_meta( get_queried_object()->post_author, 'domain', TRUE ); 

  if ( $meta !== $domain ) { // meta doesn't match, redirect
     redirect_to_original(); // function defined below
  } else {
    // meta match, only assuring that WordPress will not redirect canonical url
    remove_filter('template_redirect', 'redirect_canonical');
  }
}

Now let’s write a function to redirect request using current url, but with original domain

/**
 * Redirect the request to same url, but using original domain
 */
function redirect_to_original() {
  $original = untrailingslashit( home_url() ) . add_query_arg( array() );
  wp_safe_redirect( $original, 301 );
  exit();
}

The last thing to do is filter the permalink creation to use the user-defined domain for singular company CPT urls:

add_filter( 'post_type_link', 'custom_user_domain_plink', 999, 2 );

function custom_user_domain_plink( $post_link, $post ) {
  // we want change permalink only for company cpt posts
  if ( $post->post_type !== 'company' ) return $post_link;

  // has the user setted a custom domain? If not, do nothing
  $custom = get_user_meta( $post->post_author, 'domain', TRUE );
  if ( empty($custom) ) return $post_link;

  // let's replace the original domain, with the custom one, and return new value
  return str_replace( ORIGINAL_DOMAIN, $custom, $post_link);
}

At this point, you have only set DNS for your server, where all the user defined domains are aliases of the original.

Please note code is untested.

Method 2

A simple constant WP_SITEURL could do the trick. I did worked on something similar to it.

The difference is all of the domains were hosted on the same server
and pointed to the root directory.

The procedure i tried –

Checked the host using $_SERVER['HTTP_HOST'] and Validated if it exist on the database.
Comparing your needs, you could check this like –

global $wpdb;
$domain_user = $wpdb->get_var(
    "SELECT user_id FROM $wpdb->usermeta".
    " WHERE meta_key = 'domain'".
    " AND meta_value='". $_SERVER['HTTP_HOST'] ."'"
);
// if an user found, do further processing. 
// Exclude posts by other user using pre_get_posts may be.

Next, defined WP_SITEURL and WP_HOME

define( 'MY_SITE_DOMAIN', $_SERVER['HTTP_HOST'] );
if( !defined( 'WP_SITEURL' )):
    if( is_ssl())
        define( 'WP_SITEURL', 'https://'. MY_SITE_DOMAIN );
    else
        define( 'WP_SITEURL', 'http://'. MY_SITE_DOMAIN );
endif;

if( !defined( 'WP_HOME' ) ):
    define( 'WP_HOME', WP_SITEURL );
endif;

So, all of the links dynamically changed to current host address, and all of them were accessible as like a general wordpress site.

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0