Valid service tickets can be shorter than 32 characters.

The CAS protocol specification (http://www.jasig.org/cas/protocol),
section 3.1.1, says the following about ticket lengths:

  Services MUST be able to accept service tickets of up to 32
  characters in length. It is RECOMMENDED that services support
  service tickets of up to 256 characters in length.

This is not a requirement that tickets be at least 32 characters long,
but a requirement that services have to accept tickets at least that
long.  There appears to be no specified minimum length, so assume that
tickets have to have at least one character after the "ST-".
Merge pull request #9 from jestraw/short

Valid service tickets can be shorter than 32 characters, take 2.