Fetching OCSP responses may result in TypeError

[atmenta]

First of all, thank you for certvalidator! It makes an important task easy to complete in Python. :thumbsup:

While I was experimenting with certificate revocation status checking I ran into some issues. I'll create separate GitHub issues for those.

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When certvalidator tries to fetch OCSP responses, but the certificate to be validated does not contain any reference to OCSP responders, TypeError is raised:

TypeError: exceptions must derive from BaseException

The root of that error is that cert.ocsp_urls returns an empty list, so at the end of the following code block None is raised:

https://github.com/wbond/certvalidator/blob/5bc5c390c1955195507c23db91b8926bb03f7385/certvalidator/ocsp_client.py#L89-L109

The cert.ocsp_urls == [] case could be handled here (for safety) e.g. by raising an appropriate error, but in that case ocsp_client.fetch probably shouldn't be called at all, since it can not return any meaningful result.

[wbond]

TypeError: exceptions must derive from BaseException

Could you please provide a backtrace and the version of python you are using?

[atmenta]

Could you please provide a backtrace and the version of python you are using?

Thank you @wbond for the prompt response! Here are the answers:

$ python -V
Python 3.5.3

(Note: raise None results in the same error when Python 3.7.4 is used.)

Traceback (most recent call last):
  ...
  File "/path/to/client_certificate_validator.py", line 82, in validate
    validation_path = validator.validate_usage(key_usage)
  File "/path/to/certvalidator/certvalidator/__init__.py", line 193, in validate_usage
    self._validate_path()
  File "/path/to/certvalidator/certvalidator/__init__.py", line 121, in _validate_path
    validate_path(self._context, candidate_path)
  File "/path/to/certvalidator/certvalidator/validate.py", line 50, in validate_path
    return _validate_path(validation_context, path)
  File "/path/to/certvalidator/certvalidator/validate.py", line 387, in _validate_path
    end_entity_name_override=end_entity_name_override
  File "/path/to/certvalidator/certvalidator/validate.py", line 898, in verify_ocsp_response
    ocsp_responses = validation_context.retrieve_ocsps(cert, issuer)
  File "/path/to/certvalidator/certvalidator/context.py", line 505, in retrieve_ocsps
    **self._ocsp_fetch_params
  File "/path/to/certvalidator/certvalidator/ocsp_client.py", line 117, in fetch
    raise last_e
TypeError: exceptions must derive from BaseException