public String verifyAndExtract(String signedValue) {
    return signer.verifyAndExtract(signedValue); 
  }
Retrieves the client name from cookieString. If the cookie does not
correspond to a valid client, the function returns null.
@param cookies HTTP Request cookies.
@return Client Username if cookieString has a HS2 Generated cookie that is currently valid.
Else, returns null.
service/src/java/org/apache/hive/service/auth/HttpAuthService.java