' The CustomBasic class creates a custom Basic authentication by implementing the
' IAuthenticationModule interface. It performs the following
' tasks:
' 1) Defines and initializes the required properties.
' 2) Implements the Authenticate and PreAuthenticate methods.

Public Class CustomBasic
  Implements IAuthenticationModule

  Private m_authenticationType As String
  Private m_canPreAuthenticate As Boolean


  ' The CustomBasic constructor initializes the properties of the customized 
  ' authentication.
  Public Sub New()
    m_authenticationType = "Basic"
    m_canPreAuthenticate = False
  End Sub

  ' Define the authentication type. This type is then used to identify this
  ' custom authentication module. The default is set to Basic.

  Public ReadOnly Property AuthenticationType() As String _
   Implements IAuthenticationModule.AuthenticationType

    Get
      Return m_authenticationType
    End Get
  End Property

  ' Define the pre-authentication capabilities for the module. The default is set
  ' to false.

  Public ReadOnly Property CanPreAuthenticate() As Boolean _
   Implements IAuthenticationModule.CanPreAuthenticate


    Get
      Return m_canPreAuthenticate
    End Get
  End Property

' The checkChallenge method checks whether the challenge sent by the HttpWebRequest 
' contains the correct type (Basic) and the correct domain name. 
' Note: The challenge is in the form BASIC REALM="DOMAINNAME"; 
' the Internet Web site must reside on a server whose
' domain name is equal to DOMAINNAME.
  Public Function checkChallenge(ByVal Challenge As String, ByVal domain As String) As Boolean
    Dim challengePasses As Boolean = False

    Dim tempChallenge As [String] = Challenge.ToUpper()

    ' Verify that this is a Basic authorization request and that the requested domain
    ' is correct.
    ' Note: When the domain is an empty string, the following code only checks 
    ' whether the authorization type is Basic.
    If tempChallenge.IndexOf("BASIC") <> -1 Then
      If domain <> [String].Empty Then
        If tempChallenge.IndexOf(domain.ToUpper()) <> -1 Then
          challengePasses = True
          ' The domain is not allowed and the authorization type is Basic.
        Else
          challengePasses = False
        End If
        ' The domain is a blank string and the authorization type is Basic.
      Else
        challengePasses = True
      End If
    End If
    Return challengePasses
  End Function 'checkChallenge


  ' The PreAuthenticate method specifies whether the authentication implemented 
  ' by this class allows pre-authentication. 
  ' Even if you do not use it, this method must be implemented to obey to the rules 
  ' of interface implementation.
  ' In this case it always returns null. 
  Public Function PreAuthenticate(ByVal request As WebRequest, ByVal credentials As ICredentials) As Authorization _
      Implements IAuthenticationModule.PreAuthenticate

    Return Nothing
  End Function 'PreAuthenticate

  
  ' Authenticate is the core method for this custom authentication.
  ' When an Internet resource requests authentication, the WebRequest.GetResponse 
  ' method calls the AuthenticationManager.Authenticate method. This method, in 
  ' turn, calls the Authenticate method on each of the registered authentication
  ' modules, in the order in which they were registered. When the authentication is 
  ' complete an Authorization object is returned to the WebRequest.
  Public Function Authenticate(ByVal challenge As String, ByVal request As WebRequest, ByVal credentials As ICredentials) As Authorization _
      Implements IAuthenticationModule.Authenticate


    Dim ASCII As Encoding = Encoding.ASCII

    ' Get the username and password from the credentials
    Dim MyCreds As NetworkCredential = credentials.GetCredential(request.RequestUri, "Basic")

    If PreAuthenticate(request, credentials) Is Nothing Then
      Console.WriteLine(ControlChars.Lf + " Pre-authentication is not allowed.")
    Else
      Console.WriteLine(ControlChars.Lf + " Pre-authentication is allowed.")
    End If
    ' Verify that the challenge satisfies the authorization requirements.
    Dim challengeOk As Boolean = checkChallenge(challenge, MyCreds.Domain)

    If Not challengeOk Then
      Return Nothing
    End If

    ' Create the encrypted string according to the Basic authentication format as
    ' follows:
    ' a)Concatenate the username and password separated by colon;
    ' b)Apply ASCII encoding to obtain a stream of bytes;
    ' c)Apply Base64 encoding to this array of bytes to obtain the encoded 
    ' authorization.
    Dim BasicEncrypt As String = MyCreds.UserName + ":" + MyCreds.Password

    Dim BasicToken As String = "Basic " + Convert.ToBase64String(ASCII.GetBytes(BasicEncrypt))

    ' Create an Authorization object using the encoded authorization above.
    Dim resourceAuthorization As New Authorization(BasicToken)

    ' Get the Message property, which contains the authorization string that the 
    ' client returns to the server when accessing protected resources.
    Console.WriteLine(ControlChars.Lf + " Authorization Message:{0}", resourceAuthorization.Message)

    ' Get the Complete property, which is set to true when the authentication process 
    ' between the client and the server is finished.
    Console.WriteLine(ControlChars.Lf + " Authorization Complete:{0}", resourceAuthorization.Complete)

    Console.WriteLine(ControlChars.Lf + " Authorization ConnectionGroupId:{0}", resourceAuthorization.ConnectionGroupId)


    Return resourceAuthorization
  End Function 'Authenticate
End Class