code: function authTileLoader(fetchOptions) {
    return function(tile, src) {
      fetch(src, fetchOptions)
        .then(r => r.blob())
        .then((imgData) => {
          tile.getImage().src = URL.createObjectURL(imgData);
        })
        .catch(() => {
          console.error('Error fetchimg image at:', src);
        });
    };
  }
docs: Load a tile with full fetchOptions.
  
  This is only used when the Authorization header has been set
  in the fetchOptions.
  
  @param {Object} fetchOptions Options to use for fetch calls.
  
  @returns {Function} Tile loading function which uses fetch.