Adds rack-attack throttles

Why are these changes being introduced:

* Bots and pentesters are using a significant amount of our resources

Relevant ticket(s):

* https://mitlibraries.atlassian.net/browse/TIMX-480

How does this address that need:

* Adds a rack-attack configuration for a few scenarios
  * Overall throttle for extremely high volume (not including assets)
  * Lower throttle for redirect detected requests (these are bots
    behaving badly)
  * a few pentester bans
* campus IPs are safelisted, which should include ezproxy and vpn

Document any side effects to this change:

It's difficult to test to ensure the best tweaks to this type of work
until it is in production.

Author: JPrevost

config/initializers/rack_attack.rb

@@ -0,0 +1,121 @@
+class Rack::Attack
+
+  ### Configure Cache ###
+
+  # If you don't want to use Rails.cache (Rack::Attack's default), then
+  # configure it here.
+  #
+  # Note: The store is only used for throttling (not blocklisting and
+  # safelisting). It must implement .increment and .write like
+  # ActiveSupport::Cache::Store
+
+  # Rack::Attack.cache.store = ActiveSupport::Cache::MemoryStore.new
+
+  ### Safelist MIT IP addresses
+  # http://kb.mit.edu/confluence/x/F4DCAg
+  # Main IP range (includes campus, NAT pool, and VPNs)
+  # This also affects bot_challenge_page logic which uses rack_attack under the hood
+  Rack::Attack.safelist_ip("18.0.0.0/11")
+
+  ### Throttle Spammy Clients ###
+
+  # If any single client IP is making tons of requests, then they're
+  # probably malicious or a poorly-configured scraper. Either way, they
+  # don't deserve to hog all of the app server's CPU. Cut them off!
+  #
+  # Note: If you're serving assets through rack, those requests may be
+  # counted by rack-attack and this throttle may be activated too
+  # quickly. If so, enable the condition to exclude them from tracking.
+
+  # Throttle all requests by IP (default is 100 requests per 10 minutes)
+  #
+  # Key: "rack::attack:#{Time.now.to_i/:period}:req/ip:#{req.ip}"
+  throttle('req/ip',
+          limit: (ENV.fetch('REQUESTS_PER_PERIOD') { 100 }).to_i,
+          period: (ENV.fetch('REQUEST_PERIOD') { 10 }).to_i.minutes) do |req|
+    # don't include assets as requests
+    req.ip unless req.path.start_with?('/assets')
+  end
+
+  # Throttle redirects by IP (default is 5 per 10 minutes)
+  #
+  # Key: "rack::attack:#{Time.now.to_i/:period}:req/ip/redirects:#{req.ip}"
+  throttle('req/ip/redirects',
+          limit: (ENV.fetch('REDIRECT_REQUESTS_PER_PERIOD') { 5 }).to_i,
+          period: (ENV.fetch('REDIRECT_REQUEST_PERIOD') { 10 }).to_i.minutes) do |req|
+    req.ip if req.query_string.start_with?('geoweb-redirect')
+  end
+
+  ### Prevent Brute-Force Login Attacks ###
+
+  # The most common brute-force login attack is a brute-force password
+  # attack where an attacker simply tries a large number of emails and
+  # passwords to see if any credentials match.
+  #
+  # Another common method of attack is to use a swarm of computers with
+  # different IPs to try brute-forcing a password for a specific account.
+
+  # Throttle POST requests to /login by IP address
+  #
+  # Key: "rack::attack:#{Time.now.to_i/:period}:logins/ip:#{req.ip}"
+  # throttle('logins/ip', limit: 5, period: 20.seconds) do |req|
+  #   if req.path == '/login' && req.post?
+  #     req.ip
+  #   end
+  # end
+
+  # Throttle POST requests to /login by email param
+  #
+  # Key: "rack::attack:#{Time.now.to_i/:period}:logins/email:#{req.email}"
+  #
+  # Note: This creates a problem where a malicious user could intentionally
+  # throttle logins for another user and force their login requests to be
+  # denied, but that's not very common and shouldn't happen to you. (Knock
+  # on wood!)
+  # throttle("logins/email", limit: 5, period: 20.seconds) do |req|
+  #   if req.path == '/login' && req.post?
+  #     # return the email if present, nil otherwise
+  #     req.params['email'].presence
+  #   end
+  # end
+
+  ### Custom Throttle Response ###
+
+  # By default, Rack::Attack returns an HTTP 429 for throttled responses,
+  # which is just fine.
+  #
+  # If you want to return 503 so that the attacker might be fooled into
+  # believing that they've successfully broken your app (or you just want to
+  # customize the response), then uncomment these lines.
+  # self.throttled_response = lambda do |env|
+  #  [ 503,  # status
+  #    {},   # headers
+  #    ['']] # body
+  # end
+
+  # Block suspicious requests for '/etc/password' or wordpress specific paths.
+  # After 3 blocked requests in 10 minutes, block all requests from that IP for 5 minutes.
+  # Note: these will not show up in the throttle logs as they are blocks and not throttles
+  Rack::Attack.blocklist('fail2ban pentesters') do |req|
+    # `filter` returns truthy value if request fails, or if it's from a previously banned IP
+    # so the request is blocked
+    Rack::Attack::Fail2Ban.filter("pentesters-#{req.ip}", maxretry: 3, findtime: 10.minutes, bantime: 5.minutes) do
+      # The count for the IP is incremented if the return value is truthy
+      CGI.unescape(req.query_string) =~ %r{/etc/passwd} ||
+      req.path.include?('/etc/passwd') ||
+      req.path.include?('wp-admin') ||
+      req.path.include?('wp-login')
+    end
+  end
+
+  # Log when throttles are triggered
+  ActiveSupport::Notifications.subscribe("throttle.rack_attack") do |name, start, finish, request_id, payload|
+    @@rack_logger ||= ActiveSupport::TaggedLogging.new(Logger.new(STDOUT))
+    @@rack_logger.info{[
+      "[#{payload[:request].env['rack.attack.match_type']}]",
+      "[#{payload[:request].env['rack.attack.matched']}]",
+      "[#{payload[:request].env['rack.attack.match_discriminator']}]",
+      "[#{payload[:request].env['rack.attack.throttle_data']}]",
+      ].join(' ') }
+  end
+end