Canonical issue for captcha not working on desktop

[turt2live]

The captcha thing doesn't work on desktop due to cross-origin badness (I believe). This lead us to have a "please use a web browser" prompt instead. Recently, that prompt stopped showing up. Additionally, we have some history for these kinds of issues:

• Desktop captcha warning doesn't work on registration anymore #8287 - The web browser prompt doesn't work
• reCAPTCHA doesn't work on Riot/Desktop, so forces you to sign up on Riot/Web #4893 - Captcha shows up wrong
• Electron/Desktop: It is possible to get stuck logged in due to captcha #7617 - Cannot escape captcha

We should probably be using the fallback API here or at least providing the user with an escape route. Also, the prompt should work all the time.

Note to toml: feel free to close/reopen/whatever the other issues I've referenced. It's in your hands now.

[aaronraimist]

One solution may be to switch to a different CAPTCHA provider: #3606

[jryans]

It looks like captchas now work in Riot desktop, so I have made a change to allow them there. Hopefully that will continue to be true in production usage on all OSes.