Added error handling (unauthorized) from okta

[micromoses]

This must be done before trying to get the user,
otherwise the app yields an 400 error:

oauth2: cannot fetch token: 400 Bad Request
Response: {"error":"invalid_grant","error_description":"The authorization code is invalid or has expired."}

[micromoses]

Hi @bnfinet ,
It's been over a week, have you had a chance to take a look at this change?
Thanks!

[bnfinet]

I apologize but I have not and I won't be in a position to look at this until middle of next week.

I'm hoping to consult with @aaronpk about the Okta behavior that you are seeing. There is no current vendor specific testing in place.

[bnfinet]

Thanks for the contribution @micromoses

Just to make note here, there are also error_uri parameters and often the error parameter itself may be instructive. These parameters are not Okta specific and are part of the RFCs
https://tools.ietf.org/html/rfc6749

I'll open a ticket related to those items and general error handling.