FEATURE: improve honeypot and challenge logic

This feature amends it so instead of using one challenge and honeypot
statically per site we have a rotating honeypot and challenge value which
changes every hour.

This means you must grab a fresh copy of honeypot and challenge value once
an hour or account registration will be rejected.

We also now cycle the value of the challenge when after successful account
registration forcing an extra call to hp.json between account registrations

Client has been made aware of these changes.

Additionally this contains a JavaScript workaround for:
https://bugs.chromium.org/p/chromium/issues/detail?id=987293

This is client side code that is specific to Chrome user agent and swaps
a PASSWORD type honeypot with a TEXT type honeypot.

lib/secure_session.rb

@@ -6,15 +6,36 @@ class SecureSession
     @prefix = prefix
   end
 
+  def self.expiry
+    @expiry ||= 1.hour.to_i
+  end
+
+  def self.expiry=(val)
+    @expiry = val
+  end
+
+  def set(key, val, expires: nil)
+    expires ||= SecureSession.expiry
+    $redis.setex(prefixed_key(key), SecureSession.expiry.to_i, val.to_s)
+    true
+  end
+
   def [](key)
-    $redis.get("#{@prefix}#{key}")
+    $redis.get(prefixed_key(key))
   end
 
   def []=(key, val)
     if val == nil
-      $redis.del("#{@prefix}#{key}")
+      $redis.del(prefixed_key(key))
     else
-      $redis.setex("#{@prefix}#{key}", 1.hour, val.to_s)
+      $redis.setex(prefixed_key(key), SecureSession.expiry.to_i, val.to_s)
     end
+    val
+  end
+
+  private
+
+  def prefixed_key(key)
+    "#{@prefix}#{key}"
   end
 end