Use oauth to guard POST /answers

[subhojit777]

Next steps:

• [x] Remove GET /answers-get

[subhojit777]

Blocked because of the error

error[E0308]: match arms have incompatible types --> src/answers.rs:34:34	34	.and_then(	code	match code {	__^ 35		StatusCode::OK => { 36		let answer = answer_form.into_inner(); 37		...	47		StatusCode::FORBIDDEN => Ok(HttpResponse::Forbidden().into()),		------------------------------------ match arm with an incompatible type 48		_ => Ok(HttpResponse::NotAcceptable().into()), 49		})		_____^ expected struct futures::AndThen, found enum std::result::Result

= note: expected type futures::AndThen<futures::future::FromErr<actix_web::actix::Request<DbExecutor, models::AnswerForm>, _>, std::result::Result<actix_web::HttpResponse, _>, [closure@src/answers.rs:42:39: 45:30]> found type std::result::Result<_, _>

I think this should fix it https://stackoverflow.com/questions/53119182/conditionally-chaining-a-rust-future-based-on-initial-future-result

[subhojit777]

The above approach will not work, because conditionally it returns AndThen or Result, however, it should return only Return. And I don't think it is possible to do that here. Therefore, I have decided to move the guard check to middleware. I am following https://users.rust-lang.org/t/trouble-with-lifetimes-in-actix-web-middleware/21836 for code.