Token validity is how long a token is valid for from the time it is
created. The token will store the expiration time, that is the date when
the token expires.
so `"exp":1438209609` is actually the date in seconds when it expires.

To translate exp into a date, you would do

Date expirationDate = new Date(1438209609 * 1000l);

Here is a test case that demonstrates it

https://github.com/cloudfoundry/uaa/commit/f0c8ba99cf37855fec54b74c07ce19613c51d7e9#diff-f7a9f1a69eec2ce4278914f342d8a160R883