CUNY Academic Commons

As a final step in the newsletter plugin transition covered more in #11878 and #11647, I'm working with the CPCP (https://cpcp.commons.gc.cuny.edu/) to put a signup box in the sidebar of their homepage linked to their new Tinyletter account. The code provided by Tinyletter is below. When I try to add it as a Custom HTML widget in Wordpress, I'm told that the <form> and <input> tags aren't allowed. Perhaps we can do a workaround or simple custom widget on this? I believe there's already some code out there from others, like here: https://github.com/frebro/wp-tinyletter-widget

<form style="border:1px solid #ccc;padding:3px;text-align:center;" action="https://tinyletter.com/cpcp" method="post" target="popupwindow" onsubmit="window.open('https://tinyletter.com/cpcp', 'popupwindow', 'scrollbars=yes,width=800,height=600');return true"><p><label for="tlemail">Enter your email address</label></p><p><input type="text" style="width:140px" name="email" id="tlemail" /></p><input type="hidden" value="1" name="embed"/><input type="submit" value="Subscribe" /><p><a href="https://tinyletter.com" target="_blank">powered by TinyLetter</a></p></form>