Check that certificate is valid first

[tjzegmott]

In the first call, there is no valid cert provided and so the "x-vo-authenticated" header is missing, therefore the user is unauthenticated.

However, in the second call a valid cert is given and the header appears, hence we know that the user has been validated.

In [1]: import requests

In [2]: requests.head("https://ws-uv.canfar.net/minoc/capabilities").__dict__
Out[2]:
{'_content': b'',
 '_content_consumed': True,
 '_next': None,
 'status_code': 200,
 'headers': {'server': 'OpenCADC/cadc-rest + cadc-vosi-1.4', 'www-authenticate': 'ivoa_bearer standard_id="ivo://ivoa.net/sso#tls-with-password", access_url="https://ws-cadc.canfar.net/ac/login", Bearer, ivoa_x509 standard_id="ivo://ivoa.net/sso#BasicAA", access_url="https://ws.cadc-ccda.hia-iha.nrc-cnrc.gc.ca/cred/auth/priv", ivoa_x509', 'transfer-encoding': 'chunked', 'date': 'Thu, 20 Jun 2024 14:54:38 GMT'},
 'raw': <urllib3.response.HTTPResponse at 0x1039bac80>,
 'url': 'https://ws-uv.canfar.net/minoc/capabilities',
 'encoding': None,
 'history': [],
 'reason': '',
 'cookies': <RequestsCookieJar[]>,
 'elapsed': datetime.timedelta(microseconds=334762),
 'request': <PreparedRequest [HEAD]>,
 'connection': <requests.adapters.HTTPAdapter at 0x103564be0>}

In [3]: requests.head("https://ws-uv.canfar.net/minoc/capabilities", cert="/Users/tarikzegmott/.ssl/cadcp
   ...: roxy.pem").__dict__
Out[3]:
{'_content': b'',
 '_content_consumed': True,
 '_next': None,
 'status_code': 200,
 'headers': {'server': 'OpenCADC/cadc-rest + cadc-vosi-1.4', 'x-vo-authenticated': 'tzegmott', 'transfer-encoding': 'chunked', 'date': 'Thu, 20 Jun 2024 14:54:46 GMT'},
 'raw': <urllib3.response.HTTPResponse at 0x1039bbc40>,
 'url': 'https://ws-uv.canfar.net/minoc/capabilities',
 'encoding': None,
 'history': [],
 'reason': '',
 'cookies': <RequestsCookieJar[]>,
 'elapsed': datetime.timedelta(microseconds=427245),
 'request': <PreparedRequest [HEAD]>,
 'connection': <requests.adapters.HTTPAdapter at 0x103566cb0>}