Reference to another Drupal Website

We have multiple sites that host related content.
We would like to make a solid reference.

Entering a URL might break if the Alias is changed on the referenced site.
(And we need that bond to prepare some meta info too)

QUESTION:Is there a way to query the external Drupal site API to get the entity ID related to a pasted URL, and store the ID received from the API as a reference for link building?

Thanks