How can I send a raw HTML message without HipChat "fixing" it?

[Deleted user]

We have a URL "protocol" we handle using internal applications. Call it "asdf". E.g.:

asdf://item/orange

This produces:

<a target="_blank" rel="noopener noreferrer" href="asdf://item/orange">asdf:<wbr>/<wbr>/item<wbr>/orange</a> 

If we send the above text as a "text" message via the HipChat API v2, it is correctly identified and converted to a valid, clickable link.

However, if we send it as an "html" message, it is corrupted in any of several ways, depending on how it's sent, but the only one I really EXPECT to work is sending the anchor tag explicitly:

With a payload of:

{"message_format":"html","message":"<a href=\"asdf://item/orange\">topic</a>"}

The result is:

<a xmlns="http://www.w3.org/1999/xhtml">topic</a>

According to the API v2 documentation, this should work: 

html - Message is rendered as HTML and receives no special treatment. Must be valid HTML and entities must be escaped (e.g.: '&' instead of '&'). May contain basic tags: a, b, i, strong, em, br, img, pre, code, lists, tables.

But it looks like I'm falling victim to this API footnote:

Invalid HTML tags and attributes will be automatically removed.

How can I keep HipChat from thinking it's smarter than me, especially since the URL-ification works correctly for text messages?

[Gonchik Tsymzhitov]

I think it's obsolete request :(
Because the products Hipchat and Stride are not used anymore. 
So sad to find questions without replies.   
Sorry for the inconvenience.