anchor.diff:  Validation Protocol Version 2.0
   ===============================
   
  -## Introduction
  +== Introduction
   
   All requests are HTTP GET requests. As such, all parameters must be
   properly URL encoded.  In particular, some base64 characters (such as
  
positive.code: signature or use HTTPS connections (and verify the server
  certificate).
  
  ## Generating signatures
  
  The protocol uses HMAC-SHA-1 signatures. The HMAC key to use is the
  client API key.
  
negative.code: To avoid cut'n'paste attacks, the client MUST verify that the "otp" in
  the response is the same as the "otp" supplied in the request.
  
  == Request
  
  Construct an HTTP GET call to
  
  