Support validating tokens without an outbound network connection

[duncanmmacleod]

Currently the cvmfs-scitoken-helper cannot operate on tokens without an outbound network connection (unlike the case with X.509 credentials, which works fine). This means that tokens cannot be used for CVMFS authz for LIGO on cluster nodes that aren't exposed to the external network (eg in Cardiff).

Is it possible to support this?

FYI I posted a similar ticket for scitokens-cpp at scitokens/scitokens-cpp#97.

[DrDaveD]

This will have to wait for scitokens-cpp to add the functionality.