Is there a way to identify a user in a custom REST API method? [duplicate]

I spent two days searching for a simple way without adding plugins.

first in function.php where you define your api

//enqueue the script which will use the api
function api_callings_scripts() {
    wp_enqueue_script('score-script', get_template_directory_uri() . '/js/ScoreSaving.js', ['jquery'], NULL, TRUE);
    // Pass nonce to JS.
    wp_localize_script('score-script', 'ScoreSettings', [
      'nonce' => wp_create_nonce('wp_rest'),
    ]);
}
add_action( 'wp_enqueue_scripts', 'api_callings_scripts' ); 

Then your script Ajax call cloud be something like this

jQuery.ajax({
      type: "POST",
      url: "/wp-json/score/update",
      data: {"var1":"value1"},
      beforeSend: function(xhr) {
        xhr.setRequestHeader('X-WP-Nonce', ScoreSettings.nonce);
      },
    success: 
        function( data ) {
          console.log( data );
        }
    });

Now you can use get_current_user_id() inside your API code.