My configuration in homeserver.yaml is as follows (no quotes of any sort around the keys):
recaptcha_public_key: the_public_key
recaptcha_private_key: the_private_key
enable_registration_captcha: true
I have verified that changes in homeserver.yaml are taken into account.
I have also tested that the reCaptcha widget works by trying it out on the same domain (https://testcaptcha.the_domain.com/test for the test and https://matrix.the_domain.com for the actual matrix url).
My x_forwarded is set to true.
When I try to register a user using the Element client (formerly Riot) I get the following :
How can I get the reCaptcha widget to work properly ?
Oh I just figured this out. I found this trying to solve the problem myself. It is obvious in hindsight.
Add app.element.io or whatever domain you are running the element web client from as a legitimate source of the request. The request for the recaptcha is coming from there not from your homeserver.