Configuring Sentry as error handling service to provide additional request context

I would like to add an error handling service to my Ruby on Rails application and decided to give Sentry a try because, unlikely many other services, it has a free tier.
I am wondering if there is any of you who is experienced with Sentry configuration.
Basic configuration looks simple.
However, as the documentation in the says, “much of the usefulness of Sentry comes from additional context data with the events”.
So I would like to add to my Ruby on Rails application the code to create additional request context in Sentry’s events.
In particular I am interested in getting as much information as possible about the user experiencing the event (details, browser etc).
Where is the suggested place to put the necessary code like the Raven.user_context and Raven.tags_context methods?
I found in the documentation no more than a hint that would suggest to use a private method inside the application controller to be called with a before action filter.