Generate valid scitoken

[bbockelm]

Currently, there are a few things missing from the tokens that prevents one from actually using the demo:

1. No sub claim.
2. No kid claim. Without this, the SciTokens client library rejects the token itself.
3. No jti. Should be there for good form.

[djw8605]

For the kid claim, the new scitokens >= 1.0 should fix the bug. See scitokens/scitokens#58

For the jti, the new 1.0 version automatically makes the jti. The demo has been updated to use 1.0, and therefore there is always a new jti.

sub could be set. What should it be set to?

[bbockelm]

That PR just throws the correct exception if kid is missing, right? Doesn't actually validate things... I think?

sub can just be set to demo-user.