Log errors using slog.Logger

[maraino]

This commit allows logging errors in a slog.Logger injected in the context. This logger type is not currently used directly in step-ca, but this will change in the future.

The main change is in api/log/log.go; the rest is adapting the code to allow this.

I've considered using func Error(ctx context.Context, w http.ResponseWriter, err error), but this won't allow us to add extra things from the request to the log if we need to.

I've also had to change the render methods because they can call Error.

cc: @hslatman

[azazeal]

I think that instead of attaching a slog.Logger reference to the context.Context, we may benefit more by attaching a func. This way we can inject this concern in more elastic ways in the future.

Thoughts?

type HandlerErrorLogger func(http.ResponseWriter, *http.Request, error)

func (fn HandlerErrorLogger) call(w http.ResponseWriter, r *http.Request, err error) {
	if fn == nil {
		return // noop or use a sensible default (print to stderr via slog, etc)
	}

	fn(w, r, err)
}

func WithHandlerErrorLogger(ctx context.Context, fn HandlerErrorLogger) context.Context {
	// ...
}

func HandlerErrorLoggerFromContext(ctx context.Context) HandlerErrorLogger {
	// ...
}

func Error(rw http.ResponseWriter, r *http.Request, err error) {
	HandlerErrorLoggerFromContext(r.Context()).call(rw, r, err)
	// ...
}

Thoughts?

[maraino]

Fixed with c0b7c33