Custom error handler

[moon-stripe]

Is your feature request related to a problem? Please describe.
Similar to #1286, we use sentry for error reporting, but there don't appear to be any hooks into verdaccio to add custom error reporting middleware.

Describe the solution you'd like
To use sentry's express integration, you have to add a middleware before other middlewares, and an error-handling middleware before other error-handling middlewares. These seem like common enough use-cases that you could extend the middleware plugin api to something like:

const Sentry = require('@sentry/node');
module.exports => config => {
  Sentry.init({ dsn: config.dsn });

  return {
    before_middleware: (app) => {
      /* middleware called first */
      app.use(Sentry.Handlers.requestHandler());
    },
    register_middlewares: (app) => { /* same as current middleware api */ },
    error_middleware: (app) => {
      /* error middleware called before other error middleware */
      /* could be any custom error handler */
      app.use(Sentry.Handlers.errorHandler());
    },
  };
}

Describe alternatives you've considered

• Even just an error_middleware api that gets called after all other routes and middleware would allow for manual handling of errors:

module.exports => config => {
  Sentry.init({ dsn: config.dsn });

  return {
    error_middleware: (app) => {
      /* error middleware called before other error middleware */
      /* could be any custom error handler */
      app.use((err, req, res, next) => {
        Sentry.captureException(err);
        next(err);
      });
    },
  };
}

• Ship with sentry support that just does all of the above, by adding a direct dependency to @sentry/node or an api to pass in a sentry instance. The above middleware solution seems more flexible and easier to maintain though, and I imagine would work well for most if not all error-reporting tools.

Additional context
Thanks for verdaccio! We've had a great experience with it so far!

[juanpicado]

hi @moon-stripe I think your request makes total sense. So, I'll set a label for discussion and future development. Thanks for your detailed input.

:-) and thanks for using verdaccio, happy you are glad.