As a process I apply patches locally first, then using git upload the update(s) to a development site on the server.  Once the testing has been completed, the final step to apply the patch to the production site.   Using Terminal or your preferred shell program, navigate to the correct directory.  Then run this command using the name of the patch file (example.patch): patch < example.patchHowever, if you are patching Drupal core then remember to patch from the root directory...

You have been working hard on getting comments being added (POST) through REST in Drupal 8.  However, now you are seeing the following Assigning the wrong user against a new comment - and most likely the new comment is being assigned to the site admin.   The error here is related to the _embedded uuid. What to do You need to check that you have the correct uuid for both the entity_id and the uid entity_id -...