Auth Code Grant Callback is async and can "race" with later getTokens.

[BusterNeece]

I noticed this project's implementation of the authorization code grant is in "beta" status, but I did notice one particular issue: because it uses the Fetch API to pull the access token from the auth code, this request happens asynchronously, meaning it's entirely possible (and likely, even) that a later call to getToken on the same page will show that no token exists, because the initial auth token request hasn't had a chance to finish.

It could be that the addition of await to the Fetch calls in the auth code grant handler could resolve the issue.