Working with flask-oidc

[ashic]

I'm trying to use flask-oidc with Hydra. I've got it to the point where the user is redirected back to .../oidc_callback on the client website, which then attempts to exchange the "code" for tokens. This results in the step2_exchange of google's oauth2client to send a POST to hydra/oauth2/token

https://github.com/google/oauth2client/blob/3071457064f3705bab1b041bd624a10d5a2d2619/oauth2client/client.py#L1992

This results in the following error in Hydra:

time="2017-11-22T17:48:25Z" level=info msg="started handling request" method=POST remote="172.30.0.1:42492" request=/oauth2/token
time="2017-11-22T17:48:25Z" level=error msg="An error occurred" error="HTTP authorization header missing or invalid: The request is missing a required parameter, includes an invalid parameter value, includes a parameter more than once, or is otherwise malformed"
time="2017-11-22T17:48:25Z" level=info msg="completed handling request" measure#http://localhost:4444.latency=126861 method=POST remote="172.30.0.1:42492" request=/oauth2/token status=400 text_status="Bad Request" took="126.861µs"

I was wondering if there's a way around this problem.

[aeneasr]

Looks like that library is specifically using Google's OAuth2 flow which uses client id and secret in the post body instead of in the header which is, according to spec, not the best approach:

https://tools.ietf.org/html/rfc6749#section-2.3.1

Including the client credentials in the request-body using the two
parameters is NOT RECOMMENDED and SHOULD be limited to clients unable
to directly utilize the HTTP Basic authentication scheme (or other
password-based HTTP authentication schemes). The parameters can only
be transmitted in the request-body and MUST NOT be included in the
request URI.

You would have to make changes to the library and include the client id and secret in the authorization header using basic authorization.

[aeneasr]

It's actually funny that google does that, Golang has actually an extra variable for that: https://github.com/golang/oauth2/blob/f95fa95eaa936d9d87489b15d1d18b97c1ba9c28/internal/token.go#L92

[ashic]

Yeah... that was my thoughts too. The trouble is that I'm looking to use flask-oidc, which in turn uses google's oauth2client (which by the way, is deprecated!). Is there a setting in Hydra that would enable reading the code from the post body (since it's discouraged in the spec, but not forbidden)?

[ashic]

Christ the google library is confused! The ctor for OAuth2WebServerFlow has the option:

            authorization_header: string, For use with OAuth 2.0 providers that
                                  require a client to authenticate using a
                                  header value instead of passing client_secret
                                  in the POST body.

but factory methods like flow_from_clientsecrets have no such options.

[ashic]

The google library is encoding parameters into the body like so:

        post_data = {
            'client_id': self.client_id,
            'code': code,
            'scope': self.scope,
        }
        if self.client_secret is not None:
            post_data['client_secret'] = self.client_secret
        if self._pkce:
            post_data['code_verifier'] = self.code_verifier
        if device_flow_info is not None:
            post_data['grant_type'] = 'http://oauth.net/grant_type/device/1.0'
        else:
            post_data['grant_type'] = 'authorization_code'
            post_data['redirect_uri'] = self.redirect_uri
        body = urllib.parse.urlencode(post_data)

Could you please advise which of these is expected in the authorisation header? What would the authorisation header string look like?

[aeneasr]

See https://en.wikipedia.org/wiki/Basic_access_authentication - the client id is the username and the client secret is the password

[aeneasr]

Is there a setting in Hydra that would enable reading the code from the post body (since it's discouraged in the spec, but not forbidden)?

No, unfortunately not

[ashic]

Thanks... I was asking about what to put in the header as there seems to be support for both basic auth and bearer tokens. With basic, the code would go in the body then?

[aeneasr]

yes, only the client id and secret are incorrect, everything else stays the same

[ashic]

Right... so I'm monkey patching flask-oidc, and I've got it to include the header:

    if auth_method == 'client_secret_basic':
        basic_auth_string = '%s:%s' % (self.client_secrets['client_id'], self.client_secrets['client_secret'])
        print ("Authorization header: {}".format(basic_auth_string))
        basic_auth_bytes = bytearray(basic_auth_string, 'utf-8')
        flow.authorization_header = 'Basic %s' % b64encode(basic_auth_bytes)

Inspecting in wireshark shows https://imgur.com/a/YfEAk . However, the request still fails, and hydra logs show:

time="2017-11-23T10:54:38Z" level=info msg="started handling request" method=POST remote="172.30.0.1:48214" request=/oauth2/token
time="2017-11-23T10:54:38Z" level=error msg="An error occurred" error="HTTP authorization header missing or invalid: The request is missing a required parameter, includes an invalid parameter value, includes a parameter more than once, or is otherwise malformed"
time="2017-11-23T10:54:38Z" level=info msg="completed handling request" measure#http://localhost:4444.latency=220486 method=POST remote="172.30.0.1:48214" request=/oauth2/token status=400 text_status="Bad Request" took="220.486µs"

Do you have any pointers as to what I'm missing?

[aeneasr]

Try setting LOG_LEVEL=debug, it will give more information on what happened

[aeneasr]

Also, the header looks extremely malformed, there shouldn't be any quotes:

[ashic]

I'm guessing that's wireshark formatting. I'm trying the log level thing.

[ashic]

Nope... it's not wireshark.... it's in the string... debugging.

[ashic]

Right... the issue was with how python encoding works. I needed to change the code to:

    if auth_method == 'client_secret_basic':
        basic_auth_string = '%s:%s' % (self.client_secrets['client_id'], self.client_secrets['client_secret'])
        print ("Authorization header: {}".format(basic_auth_string))
        basic_auth_bytes = bytearray(basic_auth_string, 'utf-8')
        flow.authorization_header = 'Basic %s' % b64encode(basic_auth_bytes).decode('utf-8')

and it worked like a charm. Thanks for your continued help on this. I'll submit a PR to flask-oidc.

[aeneasr]

Nice, congratulations! :)