Fail early if the access token is not returned from GitHub

[sberyozkin]

If GitHub provider fails to complete the authorization code flow, it will reply with 200, without the actual access token, causing a confusing error when Quarkus OIDC attempts to verify this non-existent token via the UserInfo injection...

This PR adds a couple of checks to fail early and an extra check to check the confusing error

[gastaldi]

Is there anything the dev can do to fix that? (Check some URL, setting, etc?)

[sberyozkin]

Hi @gastaldi It depends on the situation, for example, in this case we saw GitHub returning GitHub specific error in JSON format with 200 response type...
Perhaps I should add Please check the logs for more details ?

[gastaldi]

That would be nice. Also if the data isn't visible in the logs, maybe point to a URL where you can find more info on how to fix that

[sberyozkin]

That is in the actual GitHub response, it includes link to the trouble shooting guide, the problem they return it with 200 which needs a debug level to be seen... Let me tune it a bit

[sberyozkin]

I gave it a try :-)

[gastaldi]

LGTM

[quarkus-bot]

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