ASP.NET

Web Services, HTTP Handlers

• The solution
  
  • the authentication mechanism based on the captcha image
    • web service udostępniający mechanizm autentykacji
    • przykładowa aplikacja ASP.NET wykorzystująca web service
  • the sample client application
    
    • the login page, Web Forms authentication
      • the name of the user
      • the password - the code from the captcha image
      • the captcha image
    • the page with information about successful login (the name of the user must by visible)
    • there should be no way to see the page with information without authentication
  • the web service
    • 3 methods:
      • int GetToken() - generates a new code and returns its identifier
      • string GetImageUrl(int token) - returns the URL to the captcha image for the specified identifier
      • bool CheckToken(int token, string value) - validates the answer for the code
    • the description of the idea:
      • the login page asks the web service for a new code during loading
        • the page receives only the identifier
        • the page does not know the code, only the web service knows it
        • the code - 6 letters from the rage 'A' - 'Z'
      • the login page asks also the web service for the URL to the captcha image (use an appropriate control and pass the URL to the control
      • the 3rd web service's methods authenticates the user; it uses the identifier (previously received from the web service and the text written by the user as parameters); it compares the text with the original one
    • the generated code expires after 3 minutes; after this time, the CheckToken() method should always return the false value
    • the GetImageUrl() method returns the URL to the HTTP handler which dynamically generates the image for the identifier; creating physical image files is forbidden; the HTTP handler is a part of the web service's project

• Hints:
  • the Login class (control), the Image class (control)
  • Page.IsPostBack, Page.Session
  • IHttpHandler interface
  • HttpContext class, Cache class
  • <authentication mode="Forms"..., <authorization...
  • http://www.mini.pw.edu.pl/~mossakow/materials/presentations/webservices.en/index.html
  • search Google for the 'captcha image'

• Approximate points:
  • the web service [5.0]
  • the client application [3.0]
  • the catcha image [2.0]