+This gets/sets the X-VPS-VITCLIENTCERTIFICATION-ID which is REQUIRED
+and defaults to "ClientCertificationIdNotSet". This is described in
+Website Payments Pro HTTPS Interface Developer's Guide as follows:
+
+"A random globally unique identifier (GUID) that is currently
+required. This requirement will be removed in the future. At this
+time, you can send any alpha-numeric ID up to 32 characters in length.
+
+NOTE: Once you have created this ID, do not change it. Use the same ID
+for every transaction."
+
+=head2 client_timeout()
+
+Timeout value, in seconds, after which this transaction should be
+aborted. Defaults to 45, the value recommended by the Website
+Payments Pro HTTPS Interface Developer's Guide.
+
+=head2 debug()
+
+Enable or disble debugging. The value specified here will also set
+$Business::OnlinePayment::HTTPS::DEBUG in submit() to aid in
+troubleshooting problems.
+
+=head2 expdate_mmyy()
+
+The expdate_mmyy() method takes a single scalar argument (typically
+the value in $content{expiration}) and attempts to parse and format
+and put the date in MMYY format as required by PayflowPro
+specification. If unable to parse the expiration date simply leave it
+as is and let the PayflowPro system attempt to handle it as-is.
+
+=head2 request_id()
+
+It is recommended that you specify your own unique request_id for each
+transaction in %content. A request_id is REQUIRED by the PayflowPro
+processor. If a request_id is not set, then Digest::MD5 is used to
+attempt to generate a request_id for a transaction.