title: Allow only HTTPS URL in input field
body: <p>I am using <a href="https://alex-d.github.io/Trumbowyg/" rel="nofollow noreferrer">Trumbowyg</a>, a WYSIWYG JavaScript editor which allows rendering images by pasting a URL.</p>
  
  <p>So you paste the URL in the field and then click the <code>Confirm</code> button and then it appends the image in the editor (<a href="https://alex-d.github.io/Trumbowyg/" rel="nofollow noreferrer">you can test it out here</a>)</p>
  
  <p>I want to prevent adding images that are not HTTPS. So if someone inserts a URL that is not HTTPS, I want to prevent appending the image when they click <code>Confirm</code>. </p>
  
  <p>This is the function for the image URL (<a href="https://github.com/Alex-D/Trumbowyg/blob/develop/src/trumbowyg.js#L1305" rel="nofollow noreferrer">from the docs</a>):</p>
  
  <pre><code>insertImage: function () {
              var t = this;
              t.saveRange();
  
              var options = {
                  url: {
                      label: 'URL',
                      required: true
                  },
                  alt: {
                      label: t.lang.description,
                      value: t.getRangeText()
                  }
              };
  
              if (t.o.imageWidthModalEdit) {
                  options.width = {};
              }
  
              t.openModalInsert(t.lang.insertImage, options, function (v) { // v are values
                  t.execCmd('insertImage', v.url);
                  var $img = $('img[src="' + v.url + '"]:not([alt])', t.$box);
                  $img.attr('alt', v.alt);
  
                  if (t.o.imageWidthModalEdit) {
                      $img.attr({
                          width: v.width
                      });
                  }
  
                  t.syncCode();
                  t.$c.trigger('tbwchange');
  
                  return true;
              });
          }
  </code></pre>
  
  <p>Any idea how I can amend this function to only allow HTTPS inputs?</p>