Apache reverse proxy not passing custom headers to the target server

Solution 1:

After experimenting I finally landed at solution that meets my needs however I must admit I have no idea why is this working the way it seems to be working.

If I add following to my configuration I can pass information I need within Authorization header.

RewriteEngine On
RewriteCond %{LA-U:REMOTE_USER} (.+)
RewriteRule .* - [E=RU:%1]
RequestHeader add Authorization %{RU}e

However other custom headers are still not showing up, and this will remain a mystery to me.

edit:

After fiddling more I discovered that as soon as I overwrite Authorization header my custom headers show up as well. Would be great to understand if this is intended behavior (maybe security feature) or a bug within mod-auth-kerb..

edit:

Anonymous user highlighted that there is a typo in KrbAuthRealsm (should be KrbAuthRealm) - I don't have access to that test rig and can't remember if I was copying/pasting or typing but since that same anonymous user decided to remove the answer I add it here as edit.