Cayan gateway guide

Adding a gateway guide

To add a Cayan gateway:

curl https://core.spreedly.com/v1/gateways.xml \
  -u 'C7cRfNJGODKh4Iu5Ox3PToKjniY:4UIuWybmdythfNGPqAqyQnYha6s451ri0fYAo4p3drZUi7q2Jf4b7HKg8etDtoKJ' \
  -H 'Content-Type: application/xml' \
  -d '<gateway>
      <gateway_type>cayan</gateway_type>
        <merchant_site_id>Your merchant site id</merchant_site_id>
        <merchant_key>Your merchant key</merchant_key>
        <merchant_name>Your merchant name</merchant_name>
      </gateway>'
<gateway>
  <token>JyDgT6epBY698oF5hUS36xwPJtH</token>
  <gateway_type>cayan</gateway_type>
  <name>Cayan</name>
  <description nil="true"/>
  <merchant_site_id>Your merchant site id</merchant_site_id>
  <merchant_name>Your merchant name</merchant_name>
  <characteristics>
    <supports_purchase type="boolean">true</supports_purchase>
    <supports_authorize type="boolean">true</supports_authorize>
    <supports_capture type="boolean">true</supports_capture>
    <supports_credit type="boolean">true</supports_credit>
    <supports_general_credit type="boolean">false</supports_general_credit>
    <supports_void type="boolean">true</supports_void>
    <supports_verify type="boolean">true</supports_verify>
    <supports_reference_purchase type="boolean">false</supports_reference_purchase>
    <supports_purchase_via_preauthorization type="boolean">false</supports_purchase_via_preauthorization>
    <supports_offsite_purchase type="boolean">false</supports_offsite_purchase>
    <supports_offsite_authorize type="boolean">false</supports_offsite_authorize>
    <supports_3dsecure_purchase type="boolean">false</supports_3dsecure_purchase>
    <supports_3dsecure_authorize type="boolean">false</supports_3dsecure_authorize>
    <supports_store type="boolean">false</supports_store>
    <supports_remove type="boolean">false</supports_remove>
    <supports_fraud_review type="boolean">false</supports_fraud_review>
    <supports_disburse type="boolean">false</supports_disburse>
  </characteristics>
  <credentials>
    <credential>
      <name>merchant_site_id</name>
      <value>Your merchant site id</value>
    </credential>
    <credential>
      <name>merchant_name</name>
      <value>Your merchant name</value>
    </credential>
  </credentials>
  <gateway_specific_fields>
  </gateway_specific_fields>
  <payment_methods>
    <payment_method>credit_card</payment_method>
  </payment_methods>
  <state>retained</state>
  <redacted type="boolean">false</redacted>
  <created_at type="dateTime">2018-06-19T17:07:27Z</created_at>
  <updated_at type="dateTime">2018-06-19T17:07:27Z</updated_at>
</gateway>