How to prevent CKEditor from removing content and tags written in source? I'd like to be able to use things such as the  tag for purposes of using font awesome icons, but CKEditor strips tags like this. If I place 
 when in 'source' mode in ckeditor it gets removed as soon as I return to the standard mode. Is there a way to ensure that ckeditor allows these tags?

I saw that someone provided a solution here How to stop CKEditor 3.6.3.7474 from stripping &lt;script&gt; tags however in drupal 8 admin/config/content/ckeditor/edit/advanced does not exist.

I also saw the CKEditorPluginConfigurableInterface here https://api.drupal.org/api/drupal/core%21modules%21ckeditor%21src%21CKEditorPluginConfigurableInterface.php/interface/CKEditorPluginConfigurableInterface/8.2.x
But I wasn't sure how to make use of that.

Is there a way to prevent CKEditor from removing content and tags written in 'source'?
I had the same requirement, I followed this tutorial for that, How to Display Icons in Drupal using Icon API.

It needs two modules (1) Fontawesome and its dependencies Library module &amp; Fontawesome Library. (2) Other module you need is Icon API which has sub-module Icon_filter that will convert the icons in the images.

I am afraid that Icon API module will work for D8 or not, but it has D8 version but unstable as you can see on the module page.

I am using this way on D7 site.

Update: Filter setting