Add Proof Key for Code Exchange Support

[TBryant13]

Is your feature request related to a problem? Please describe.
I am not able to authenticate via Okta because Okta only supports Authorization Code Flow with PKCE.

Describe the solution you'd like
Add Proof Key for Code Exchange support. There is a flag for it in Swagger UI 3.24.0+. The flag in Swagger UI is usePkceWithAuthorizationCodeGrant.

Additional context
Here is a similar issue in Springfox: springfox/springfox#3005

[td-edge]

This would be a nice addition since implicit flow is considered antiquated now.

👍

[ubogdan]

Since this is a Swagger-UI related issue, I believe you should open a feature request on the proper HTTP handler you need it. https://github.com/swaggo/gin-swagger, https://github.com/swaggo/echo-swagger https://github.com/swaggo/http-swagger