Specify the type of error content when the key cannot be extracted

[TheAwiteb]

Providing the possibility to specify the type of error content when the key cannot be extracted would be great, because it would allow to return json, html or xml.

But I think that will generate breaking changes, how do you think we can add it?

https://github.com/AaronErhardt/actix-governor/blob/main/src/key_extractor.rs#L18-L21

[TheAwiteb]

Maybe we need to do something like this and remove response_error from KeyExtractor

use actix_web::http::{header::ContentType, StatusCode};

trait Foo {
    type Content: ToString;

    fn content(&self) -> (Self::Content, ContentType);

    fn status(&self) -> StatusCode;
}

trait KeyExtractor: Clone {
    type KeyExtractionError: Foo;

    // ...
}

[AaronErhardt]

I think we should eventually clean up the KeyExtractor trait and change the extract method to return Result<Self::Key, actic_web::HttpResponse instead of Result<Self::Key, Self::KeyExtractionError>. This allows you to have maximum flexibility for the response that is returned in case of an error. This would also allow us to remove the response_error method.

Also, response_error_content could simply get a HttpResponseBuilder and return a HttpResponse for more flexibility.