Icons.php

<?php
   return [
       // icon identifier
       'mysvgicon' => [
            // icon provider class
           'provider' => \TYPO3\CMS\Core\Imaging\IconProvider\SvgIconProvider::class,
            // the source SVG for the SvgIconProvider
           'source' => 'EXT:my_extension/Resources/Public/Icons/mysvg.svg',
       ],
       'mybitmapicon' => [
           'provider' => \TYPO3\CMS\Core\Imaging\IconProvider\BitmapIconProvider::class,
            // the source bitmap file
           'source' => 'EXT:my_extension/Resources/Public/Icons/mybitmap.png',
       ],
       'myfontawesomeicon' => [
           'provider' => \TYPO3\CMS\Core\Imaging\IconProvider\FontawesomeIconProvider::class,
            // the fontawesome icon name
           'name' => 'spinner',
            // all icon providers provide the possibility to register an icon that spins
           'spinning' => true,
       ],
   ];