Allow extra form attributes to be added to OIDC callback

[ChrisSamo632]

Content & configuration

Swagger/OpenAPI definition:

FastAPI generated swagger ui using OAS 3.1

Is your feature request related to a problem?

Some OIDC IdP services require additional fields to be sent to the token endpoint in order to generate appropriate Access Tokens, e.g. LogTo, which returns an opaque token rather than a JWT unless a resource is specified along with the scope.

Describe the solution you'd like

The ability to dynamically add extra fields to the OIDC token (and maybe authorisation) forms, e.g. https://github.com/swagger-api/swagger-ui/blob/master/src/core/plugins/auth/actions.js#L142

Describe alternatives you've considered

Additional context