anchor.diff:   * Base 64 encode the resulting value according to RFC 4648, for example, `t2ZMtKeValdA+H0jVpj3LIichn4=`.
    * Append the value under key 'h' to the message. 
   
  -## Verifying signatures
  +== Verifying signatures
   
   To verify a signature on a response message, follow the same procedure
   that was used to sign the response message and compare the signature
  
positive.code: 
  An example request:
  
  ```
  http://api.yubico.com/wsapi/2.0/verify?otp=vvvvvvcucrlcietctckflvnncdgckubflugerlnr&id=87&timeout=8&sl=50&nonce=askjdnkajsndjkasndkjsnad
  ```
  
  And if you require additional information on timestamp and session
  counters:
  
  ```
  http://api.yubico.com/wsapi/2.0/verify?id=87&otp=vvvvvvcucrlcietctckflvnncdgckubflugerlnr&timeout=8&sl=50&nonce=askjdnkajsndjkasndkjsnad&timestamp=1
  ```
  
  ## Response
  
  The verification response tells you whether the OTP is valid.  The
  response has the following values:
  
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
  
  