[autoendpoint] Add sentry support to web handlers

[AzureMarker]

Top-level panics are caught by sentry already, but panics and other errors in Actix handlers are caught at the worker level by Actix instead of sentry.

Some possible solutions:

• https://docs.rs/sentry-actix/
  It's not clear if this library will catch errors thrown by other middleware, but perhaps this isn't important if we don't use other middleware.
• https://github.com/mozilla-services/syncstorage-rs/blob/master/src/web/middleware/sentry.rs
  Already in use by syncstorage, handles errors thrown by other middleware, but is kind of a hack.

[jrconlin]

Yeah, the sentry middleware is definitely a hack. The original actix author felt that errors should not progress into the middleware and should be handled by the functions. I don't know if that issue will be re-opened now that the project is under different management.

[pjenvey]

actix-web middleware is just not super friendly to use as of actix-web 1.0.

They require some extra boilerplate to use (the Transform), use their own ServiceRequest/ServiceResponse (vs the regular HttpRequest/Response) which can be limiting particularly once they're consumed by calling into the wrapped middleware (e.g. self.service.call(sevice_request)).

With all these drawbacks + the strange error handling, I generally don't recommend using actix-web middlewares at all unless there's a very compelling reason and or it's for something very simple.

[AzureMarker]

Using extractors (FromRequest) may be a better way to achieve some of what we need.

[AzureMarker]

sentry-actix does not support Actix 1.0, so we may have to re-use our "hack" middleware:
getsentry/sentry-rust#143

[AzureMarker]

This issue is now deprioritized, but here are some learnings:

• sentry 0.18 does not support std::error::Error, and some useful utilities (i.e. backtrace_to_stacktrace) are private. sentry 0.19 fixes most of these problems. We need to upgrade sentry before this issue can be completed.
• sentry 0.19 splits into multiple crates (sentry-core, sentry-backtrace, etc). The sentry crate combines these and acts like the 0.18 version (feature flags to select features). We should continue to use the sentry crate because it provides the transport integrations (curl).
• Since sentry-actix does not work with Actix 1.0, we need to write our own middleware. The one used in syncstorage-rs is complicated by support for errors in middleware. We can make a simpler sentry middleware by not supporting errors in middleware.
• We can write our own Sentry Actix middleware pretty easily via App::wrap_fn:

  App::new().wrap_fn(sentry_middleware)
  
  // ...
  
  fn sentry_middleware(
      req: ServiceRequest,
      service: &mut impl Service<
          Request = ServiceRequest,
          Response = ServiceResponse,
          Error = actix_web::Error,
      >,
  ) -> impl Future<Output = Result<ServiceResponse, actix_web::Error>> {
      let response = service.call(req);
  
      async move {
          let response: Result<ServiceResponse, actix_web::Error> = response.await;
          // Check for error and send to sentry
          response
      }
  }

[AzureMarker]

Bumped to 5 due to sentry not working with Actix 1.0/2.0. We need to make our own middleware.