After updating from Tomcat 8.0.28 to Tomcat 8.0.30 the login form of cms and console fails with an empty page and a cryptic query:
Reverting to Tomcat 8.0.28 or Tomcat 8.29 will fix this issue. But for security reasons we have to update in the near future. So it's a critical bug!
There is one workaround:
The log tells that the user is logged in successfully. So, removing the query and reloading the page manually will show the cms oder console as a logged in user. But that is hard to communicate towards the users.
Possible occasion may be the fix https://bz.apache.org/bugzilla/show_bug.cgi?id=56917 (see release notes of tomcat).