Builds the Challenge Request (CReq) for browser-based flow.
The GetChallengeRequest method is used to build the Challenge Request (CReq) which will be sent in a form post to the ACSURL property via the cardholder browser.
An iframe should be created in the cardholder's browser, which will be used to send the challenge request and allow the cardholder and ACS to interact directly.
The size of the challenge window (iframe) may be any of the sizes listed in ChallengeWindowSize. Before calling this method set ChallengeWindowSize to the appropriate value to let the ACS know the size of the window on the cardholder's browser.
Calling this method will return a string which should be placed in a creq form variable.
The SessionData setting may also be set with any data that may be helpful to continue processing the transaction after the final challenge response is received at the NotificationURL. To prepare the session data for submission, query EncodedSessionData. The encoded string may then be placed in the threeDSSessionData form variable.
Note: The maximum length of the threeDSSessionData form variable, after being encoded, is 1024 bytes.
Once the challenge has been completed by the cardholder, the directory server will post a Results Request (RReq) to the ResultsURL specified when calling SendAuthRequest. See CheckResponse and GetResultsResponse for more details.
The ACS will also post the Challenge Response to the NotificationURL specified when calling SendAuthRequest. This post contains data which may be parsed to verify the challenge results. See CheckResponse for more details.