Return a token from auth._refreshBearerToken

[eatyourgreens]

Return the refreshed token, or an empty string, from auth._refreshBearerToken(). This should fix token-handling for code that expects auth.checkBearerToken() to return a valid token.

[camallen]

code changes LGTM.

OOI - did you run this locally in FEM app for testing?

For release - I assume this is a bug fix / patch version bump as we haven't changed the API of this client library function. I can't see this causing issues in PFE land but i'm not sure about other apps (do they use oauth?)... should we consider a major release and opt in?

[eatyourgreens]

I haven't run this with the new classifier yet. I'll have a look. Maybe I can hack the dev classifier so that it always refreshes the token when it makes a classification.

[eatyourgreens]

I think 3.3.4 should be ok for release. Anything that's checking the return value of auth.checkBearerToken() expects a falsy value to indicate that you aren't logged in.

[eatyourgreens]

Setting up the monorepo's dev classifier to use this client turned out to be more work than I thought, but I've confirmed that it works with the changes here.

[eatyourgreens]

Fixes #148.