handler for token renewal

[dgregoire]

What would you think of having a on handler for when the module renews a token? Different use cases for this, the most obvious one (I think) being some sort of wired reaction - such as updating some data in some database.

[ahmedsakr]

I think it's very appropriate now that the library has implicit refreshing of tokens (if left enabled through the config module). Should be simple enough to support too.

[dgregoire]

@ahmedsakr I can PR this one once you're done with #93

[ahmedsakr]

@dgregoire Amazing, that'd be great! I wanted to ask you: how do we plan on "identifying" which tokens were renewed? The library does not store any information about the session other than the tokens, and I presume you would want to have logic in the refresh handler that would update the session information for the specific user.

[dgregoire]

I was holding off on #93 before I look at it more seriously, assuming you're going to make significant changes - probably something like register a on closure for each new client()?