fix: fix check for 'internal_failure' condition

[georgysavva]

As I was saying in this comment
In some cases response doesn't contain error_description field. So the retry won't work. The solution is to look at both error and error_description fields.

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[georgysavva]

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[software-dov]

This changes the test coverage: in test__token_endpoint_request_internal_failure_error, the first check should only have "error_description" set. Otherwise looks good.

[software-dov]

LGTM. Test could be refactored to loop over "error" and "error_description", but it's fine as is.

[georgysavva]

Fixed the test

[busunkim96]

@georgysavva Thank you for submitting a patch!

[ziliangpeng]

@georgysavva Do you think it's possible that, sometimes if we get errors from the server, the response will not be in json format, thus loading json from the response before checking ok would cause exception?

[georgysavva]

@ziliangpeng totally makes sense. Should be a good improvement. Fill free to open a PR with the fix.