[PLATFORM-1195]: rfc8414 compliance

[MaeIsBad]

https://prima-assicurazioni-spa.myjetbrains.com/youtrack/issue/PLATFORM-1195

[cottinisimone]

Don't like so much to have a string replicated. Can we change how routings are made and instead of using service and #[post macro use this kind of build pattern?

web::resource(controller::token::ENDPOINT)
        .route(web::post().to(controller::token)))

[MaeIsBad]

I don't really like that, it's quite ugly. I don't like repeating the string either, but I prefer doing it this way

for reference, here is a cleaned up version of the #[post] macro

struct token;
impl HttpServiceFactory for token {
    fn register(self, cfg: &mut actix_web::dev::AppService) {
        /// Generate a new jwt token for a given audience. For `client_credentials` the audience is found in the post body
        /// and for `authorization_code` the audience is found in the authorizations cache.
        /// All the permissions found in the local store will be included in the generated token.
        async fn token(
            app_data: Data<AppData>,
            token_request: Either<Json<TokenRequest>, Form<TokenRequest>>,
        ) -> HttpResponse {
            let (
                Either::Left(Json(token_request))
                | Either::Right(Form(token_request))
            ) = token_request;
            match token_request {
                TokenRequest::ClientCredentials(request) => {
                    jwt_for_client_credentials(app_data, request).await
                }
                TokenRequest::AuthorizationCode(request) => {
                    jwt_for_authorization_code(app_data, request).await
                }
            }
        }
        let res = Resource::new("/oauth/token")
            .name("token")
            .guard(::actix_web::guard::Post())
            .to(token);
        HttpServiceFactory::register(res, cfg)
    }
}