Find a json/dict of the client certificate from a HTTPS request

Question

I'm having a client certificate - server certificate for a Flask endpoint i'm building. Currently the HTTPS requests can go though, and I can print the details of the client certificate on the server side like this:

@app.route('/predict', methods=['POST'])
def predict():
    res = "hi"
    status = False

    if request.url.startswith('https://'):
        client_cert = request.headers["CLIENT_CERT"]
        res = client_cert["subject"]
        print(client_cert)

It prints out the info of the client cert that comes from a request:

"{'subject': ((('countryName', 'DE'),), (('stateOrProvinceName', 'BW'),), (('localityName', 'Walldorf'),), (('organizationName', 'MYCOMPANY'),), (('organizationalUnitName', 'MYDEPARTMENT'),), (('commonName', '*.domainname.com'),)), 'issuer': ((('countryName', 'DE'),), (('stateOrProvinceName', 'BW'),), (('localityName', 'Walldorf'),), (('organizationName', 'MYCOMPANY'),), (('organizationalUnitName', 'MYDEPARTMENT'),), (('commonName', 'SAMPLE CA'),)), 'version': 1, 'serialNumber': '01', 'notBefore': 'Aug 12 07:21:25 2021 GMT', 'notAfter': 'Aug 12 07:21:25 2022 GMT'}"

I am looking to retrieve the commonName entry in the above string to do further verification, as I only want to allow commonName that is in a particular format that I expect.

As you can see, retrieving the client cert from the headers of the request gives the certificate in the form of a string. Because this is not a string of proper json, I cannot use json.loads to parse the string into a dictionary. is there any good way to parse this string so that I can get the commonName value, or is there any other good way to access the client certificate of a request?

Thanks!

Answer 1

The format of the response appears to be well-defined. In which case, this will achieve the OP's objective. There's undoubtedly a RE that will do the trick but this is simple and effective:-

def getCommonNames(s):
    rv = []
    offset = 0
    try:
        while True:
            i = s.index('commonName', offset)
            offset = i + 14
            j = s.index("'", offset)
            rv.append(s[offset:j])
    except Exception:
        pass
    return rv


S = "{'subject': ((('countryName', 'DE'),), (('stateOrProvinceName', 'BW'),), (('localityName', 'Walldorf'),), (('organizationName', 'MYCOMPANY'),), (('organizationalUnitName', 'MYDEPARTMENT'),), (('commonName', '*.domainname.com'),)), 'issuer': ((('countryName', 'DE'),), (('stateOrProvinceName', 'BW'),), (('localityName', 'Walldorf'),), (('organizationName', 'MYCOMPANY'),), (('organizationalUnitName', 'MYDEPARTMENT'),), (('commonName', 'SAMPLE CA'),)), 'version': 1, 'serialNumber': '01', 'notBefore': 'Aug 12 07:21:25 2021 GMT', 'notAfter': 'Aug 12 07:21:25 2022 GMT'}"
print(getCommonNames(S))