Support form_post OIDC response mode about oidc

[hifabienne]

hei @livio-a @muhlemmer what do you think about this?

[muhlemmer]

The OpenID connect standard is this one: https://openid.net/specs/oauth-v2-form-post-response-mode-1_0.html

Instead to sending a typical redirect to the client's callback we would respond with a html <form> that auto-submits to the token endpoint. The form data holds the same data as the redirected URL would.

Overall complexity would be low to implement in OIDC. However, I don't see this being high priority at the moment.

I will migrate this to the OIDC repository as it needs to be implemented there.

[hifabienne]

Thank you for sharing your idea.
If there is a significant demand from customers/community, we will carefully consider implementing the feature.
Currently, the issue will be added to our product backlog to collect feedback.

Meanwhile, if you're interested in implementing it yourself, we also welcome pull requests.

[ay4toh5i]

@muhlemmer @livio-a
Hey, I attempted an implementation of form_post as a trial. How does it look?
Here it is #551.