def get_access_token()

in LambdaFunction/FHIRClient.py [0:0]

• 43 lines of code
• 2 McCabe index (conditional complexity)

    def get_access_token(self, clientid, audience, expires_in_minutes=4):
        segments = []

        header_dict = {
          "alg": "RS384",
          "typ": "JWT"
        }
        header = json.dumps(header_dict, separators=(",", ":")).encode("utf-8")
        segments.append( base64.urlsafe_b64encode(header).replace(b"=", b"") )

        tmpexp = datetime.now(timezone.utc) + timedelta(minutes=expires_in_minutes)
        tmpintexp = int((tmpexp - datetime(1970, 1, 1, tzinfo=timezone.utc)).total_seconds())
        payload_dict = {
            'iss': clientid,
            'sub': clientid,
            'aud': audience,
            'jti': ''.join(random.choice(string.ascii_letters) for i in range(150)),
            'exp': tmpintexp
        }
        payload = json.dumps(payload_dict, separators=(",", ":")).encode("utf-8")
        segments.append( base64.urlsafe_b64encode(payload).replace(b"=", b"") )
        signing_input = b".".join(segments)
        logger.debug('signing input: {}'.format(signing_input.decode("utf-8")))

        response = self.kms_client.sign(
            KeyId=self.kms_key_id,
            Message=signing_input,
            MessageType='RAW',
            SigningAlgorithm='RSASSA_PKCS1_V1_5_SHA_384'      ## 'RSASSA_PSS_SHA_384'|'ECDSA_SHA_384'
        )
        signature = base64.urlsafe_b64encode(response['Signature']).replace(b"=", b"")
        logger.debug('signature: {}'.format( signature ))
        segments.append( signature )
        encoded = b".".join(segments)
        logger.debug('encoded: {}'.format(encoded.decode("utf-8")))
        
        postData = {
            'grant_type' : 'client_credentials',
            'client_assertion_type': 'urn:ietf:params:oauth:client-assertion-type:jwt-bearer',
            'client_assertion': encoded
        };
        r = self.http.request('POST', audience, fields=postData)
        logger.debug(json.loads(r.data.decode()))
        
        return {
            'status': r.status,
            'data': json.loads(r.data.decode())
        }