def get_purchase_params(cart, callback_url=None, extra_data=None):
    """
    This method will build out a dictionary of parameters needed by CyberSource to complete the transaction

    Args:
        cart (Order): The order model representing items in the user's cart.

    Keyword Args:
        callback_url (unicode): The URL that CyberSource should POST to when the user
            completes a purchase.  If not provided, then CyberSource will use
            the URL provided by the administrator of the account
            (CyberSource config, not LMS config).

        extra_data (list): Additional data to include as merchant-defined data fields.

    Returns:
        dict

    """
    total_cost = cart.total_cost
    amount = "{0:0.2f}".format(total_cost)
    params = OrderedDict()

    params["amount"] = amount
    params["currency"] = cart.currency
    params["orderNumber"] = "OrderId: {0:d}".format(cart.id)

    params["access_key"] = get_processor_config().get("ACCESS_KEY", "")
    params["profile_id"] = get_processor_config().get("PROFILE_ID", "")
    params["reference_number"] = cart.id
    params["transaction_type"] = "sale"

    params["locale"] = "en"
    params["signed_date_time"] = datetime.utcnow().strftime("%Y-%m-%dT%H:%M:%SZ")
    params[
        "signed_field_names"
    ] = "access_key,profile_id,amount,currency,transaction_type,reference_number,signed_date_time,locale,transaction_uuid,signed_field_names,unsigned_field_names,orderNumber"
    params["unsigned_field_names"] = ""
    params["transaction_uuid"] = uuid.uuid4().hex
    params["payment_method"] = "card"

    if callback_url is not None:
        params["override_custom_receipt_page"] = callback_url
        params["override_custom_cancel_page"] = callback_url

    if extra_data is not None:
        # CyberSource allows us to send additional data in "merchant defined data" fields
        for num, item in enumerate(extra_data, start=1):
            key = u"merchant_defined_data{num}".format(num=num)
            params[key] = item

    return params

def get_purchase_endpoint():
    """
    Return the URL of the payment end-point for LiqPay.
    Returns:
        unicode
    """
    return get_processor_config().get('PURCHASE_ENDPOINT', '')

def processor_hash(value):
    """
    Performs the base64(HMAC_SHA1(key, value)) used by CyberSource Hosted Order Page
    """
    shared_secret = get_processor_config().get('SHARED_SECRET', '')
    hash_obj = hmac.new(shared_secret.encode('utf-8'), value.encode('utf-8'), sha1)
    return binascii.b2a_base64(hash_obj.digest())[:-1]  # last character is a '\n', which we don't want

def get_purchase_endpoint():
    """
    Return the URL of the payment end-point for CyberSource.

    Returns:
        unicode

    """
    return get_processor_config().get("PURCHASE_ENDPOINT", "")

def get_purchase_params(cart, callback_url=None):
    """
    This method will build out a dictionary of parameters needed by CyberSource to complete the transaction

    Args:
        cart (Order): The order model representing items in the user's cart.

    Keyword Args:
        callback_url (unicode): The URL that CyberSource should POST to when the user
            completes a purchase.  If not provided, then CyberSource will use
            the URL provided by the administrator of the account
            (CyberSource config, not LMS config).

    Returns:
        dict

    """
    total_cost = cart.total_cost
    amount = "{0:0.2f}".format(total_cost)
    params = OrderedDict()

    params['amount'] = amount
    params['currency'] = cart.currency
    params['orderNumber'] = "OrderId: {0:d}".format(cart.id)

    params['access_key'] = get_processor_config().get('ACCESS_KEY', '')
    params['profile_id'] = get_processor_config().get('PROFILE_ID', '')
    params['reference_number'] = cart.id
    params['transaction_type'] = 'sale'

    params['locale'] = 'en'
    params['signed_date_time'] =  datetime.utcnow().strftime('%Y-%m-%dT%H:%M:%SZ')
    params['signed_field_names'] = 'access_key,profile_id,amount,currency,transaction_type,reference_number,signed_date_time,locale,transaction_uuid,signed_field_names,unsigned_field_names,orderNumber'
    params['unsigned_field_names'] = ''
    params['transaction_uuid'] = uuid.uuid4().hex
    params['payment_method'] = 'card'

    if callback_url is not None:
        params['override_custom_receipt_page'] = callback_url
        params['override_custom_cancel_page'] = callback_url

    return params

def sign(params, signed_fields_key='orderPage_signedFields', full_sig_key='orderPage_signaturePublic'):
    """
    params needs to be an ordered dict, b/c cybersource documentation states that order is important.
    Reverse engineered from PHP version provided by cybersource
    """
    merchant_id = get_processor_config().get('MERCHANT_ID', '')
    order_page_version = get_processor_config().get('ORDERPAGE_VERSION', '7')
    serial_number = get_processor_config().get('SERIAL_NUMBER', '')

    params['merchantID'] = merchant_id
    params['orderPage_timestamp'] = int(time.time() * 1000)
    params['orderPage_version'] = order_page_version
    params['orderPage_serialNumber'] = serial_number
    fields = u",".join(params.keys())
    values = u",".join([u"{0}={1}".format(i, params[i]) for i in params.keys()])
    fields_sig = processor_hash(fields)
    values += u",signedFieldsPublicSignature=" + fields_sig
    params[full_sig_key] = processor_hash(values)
    params[signed_fields_key] = fields

    return params

def processor_hash(value):
    """
    Calculate the base64-encoded, SHA-1 hash used by LiqPay.

    Args:
        value (string): The value to encode.

    Returns:
        string

    """
    secret_key = get_processor_config().get('SECRET_KEY', '')
    return base64.b64encode(sha1(secret_key + value + secret_key).digest())

def processor_hash(value):
    """
    Calculate the base64-encoded, SHA-256 hash used by CyberSource.

    Args:
        value (string): The value to encode.

    Returns:
        string

    """
    secret_key = get_processor_config().get("SECRET_KEY", "")
    hash_obj = hmac.new(secret_key.encode("utf-8"), value.encode("utf-8"), sha256)
    return binascii.b2a_base64(hash_obj.digest())[:-1]  # last character is a '\n', which we don't want

def processor_hash(value):
    """
    Calculate the base64-encoded, SHA-256 hash used by CyberSource.

    Args:
        value (string): The value to encode.

    Returns:
        string

    """
    private_key = get_processor_config().get('PRIVATE_KEY', None)
    if not private_key:
        raise CCProcessorPrivateKeyAbsenceException()
    return base64.b64encode(sha.new(private_key + value + private_key).digest())

def get_purchase_params(cart, callback_url=None, extra_data=None):
    """
    Just stub for now
    """
    total_cost = cart.total_cost
    amount = "{0:0.2f}".format(total_cost)
    params = OrderedDict()

    params['amount'] = amount
    params['currency'] = cart.currency
    params['orderNumber'] = "OrderId: {0:d}".format(cart.id)

    params['access_key'] = get_processor_config().get('ACCESS_KEY', '')
    params['profile_id'] = get_processor_config().get('PROFILE_ID', '')
    params['reference_number'] = cart.id
    params['transaction_type'] = 'sale'

    params['locale'] = 'en'
    params['signed_date_time'] = datetime.utcnow().strftime('%Y-%m-%dT%H:%M:%SZ')
    params['signed_field_names'] = 'access_key,profile_id,amount,currency,transaction_type,reference_number,signed_date_time,locale,transaction_uuid,signed_field_names,unsigned_field_names,orderNumber'
    params['unsigned_field_names'] = ''
    params['transaction_uuid'] = uuid.uuid4().hex
    params['payment_method'] = 'card'
    params['success'] = True

    if callback_url is not None:
        params['override_custom_receipt_page'] = callback_url
        params['override_custom_cancel_page'] = callback_url

    if extra_data is not None:
        # CyberSource allows us to send additional data in "merchant defined data" fields
        for num, item in enumerate(extra_data, start=1):
            key = u"merchant_defined_data{num}".format(num=num)
            params[key] = item

    return params

 def test_site_override_settings(self):
     self.assertEqual(get_processor_config()['MERCHANT_ID'], 'edx_test_override')
     self.assertEqual(get_processor_config()['SHARED_SECRET'], 'secret_override')

def get_purchase_endpoint():
    return get_processor_config().get('PURCHASE_ENDPOINT', '')

def get_purchase_params(cart, callback_url=None, extra_data=None):
    """
    This method will build out a dictionary of parameters needed by CyberSource to complete the transaction
    Args:
        cart (Order): The order model representing items in the user's cart.
    Keyword Args:
        callback_url (unicode): The URL that CyberSource should POST to when the user
            completes a purchase.  If not provided, then CyberSource will use
            the URL provided by the administrator of the account
            (CyberSource config, not LMS config).
        extra_data (list): Additional data to include as merchant-defined data fields.
    Returns:
        dict
    """
    site_name = microsite.get_value('SITE_NAME', settings.SITE_NAME)
    total_cost = cart.total_cost
    amount = "{0:0.2f}".format(total_cost)
    params = OrderedDict()

    params['version'] = 3
    course = get_course_by_id(SlashSeparatedCourseKey.from_deprecated_string(extra_data[0]))
    course_name = course.display_name_with_default

    '{base_url}{dashboard}'.format(
        base_url=site_name,
        dashboard=reverse('dashboard'))
    params['description'] = u'Запис на курс "{course_name}" ({course_num}) | Номер заказу [{course_id}]'.format(
        course_name=course_name,
        course_num=extra_data[0],
        course_id=cart.id
    )

    params['amount'] = amount
    params['currency'] = "uah"
    params['orderNumber'] = "OrderId: {0:d}".format(cart.id)

    params['signed_date_time'] = datetime.utcnow().strftime('%Y-%m-%dT%H:%M:%SZ')

    params['course_id'] = extra_data[0]

    params['course_name'] = course_name

    params['public_key'] = get_processor_config().get('PUBLIC_KEY', '')
    params['type'] = 'buy'

    params['language'] = 'ru'
    # params['signed_date_time'] = datetime.utcnow().strftime('%Y-%m-%dT%H:%M:%SZ')

    if callback_url is not None:
        params['server_url'] = callback_url

    params['server_url'] = get_processor_config().get('SERVER_URL', 'https://59065b71.ngrok.com/shoppingcart/postpay_callback/')
    params['result_url'] = '{base_url}{dashboard}'.format(
        base_url=site_name,
        dashboard=reverse('dashboard'))
    if get_processor_config().get('SANDBOX') or course_name == "sandbox":
        params['sandbox'] = 1

    if callback_url is not None:
        params['override_custom_receipt_page'] = callback_url
        params['override_custom_cancel_page'] = callback_url

    if extra_data is not None:
        # LiqPay allows us to send additional data in "merchant defined data" fields
        for num, item in enumerate(extra_data, start=1):
            key = u"merchant_defined_data{num}".format(num=num)
            params[key] = item

    return params