Process untrusted, expired or not-match certificates with HttpWebRequest and ASP.Net 

Imports System.Net
Imports System.Web
Imports System.Security.Cryptography.X509Certificates
Imports System.Runtime.InteropServices

Public Class MyAcceptCertificatePolicy
  Implements ICertificatePolicy

  Private Enum eCertificateProblem As Integer
    CertNone = 0
    CertEXPIRED = &H800B0101
    CertVALIDITYPERIODNESTING = &H800B0102
    CertROLE = &H800B0103
    CertPATHLENCONST = &H800B0104
    CertCRITICAL = &H800B0105
    CertPURPOSE = &H800B0106
    CertISSUERCHAINING = &H800B0107
    CertMALFORMED = &H800B0108
    CertUNTRUSTEDROOT = &H800B0109
    CertCHAINING = &H800B010A
    CertREVOKED = &H800B010C
    CertUNTRUSTEDTESTROOT = &H800B010D
    CertREVOCATION_FAILURE = &H800B010E
    CertCN_NO_MATCH = &H800B010F
    CertWRONG_USAGE = &H800B0110
    CertUNTRUSTEDCA = &H800B0112
  End Enum

  Public Overridable Function CheckValidationResult( _
   ByVal srvPoint As ServicePoint, _
   ByVal certificate As X509Certificate, _
   ByVal request As WebRequest, _
   ByVal certificateProblem As Integer) As Boolean _
    Implements ICertificatePolicy.CheckValidationResult

    Dim cp As eCertificateProblem = certificateProblem

    'this accepts certificates with untrusted root, 
    '  And If cn does Not match host name
    Select Case cp
      Case eCertificateProblem.CertUNTRUSTEDROOT, _
           eCertificateProblem.CertCN_NO_MATCH
        Return True
      Case eCertificateProblem.CertNone
        Return True
    End Select
    Return False
  End Function
End Class

Public Class Conector
  Public Shared Function GetEncodingFromCT(ByRef ContentType As String) As String
    On Error Resume Next
    Return Split(ContentType, "charset=", 2, CompareMethod.Text)(1).Trim("""")
  End Function

  Public Function GetWebData(ByVal URL As String) As String
    ServicePointManager.CertificatePolicy = New MyAcceptCertificatePolicy

    'create a web request To the URL
    Dim Req As HttpWebRequest = HttpWebRequest.Create(URL)

    'get a response from web site
    Dim Response As HttpWebResponse = Req.GetResponse()

    'check encoding of the response.
    Dim sEncoding As String = response.ContentEncoding
    If Len(sEncoding) = 0 Then sEncoding = GetEncodingFromCT(Response.ContentType)

    'read the response stream To end using the response stream
    Dim Reader As New StreamReader(Response.GetResponseStream(), _
      System.Text.Encoding.GetEncoding(sEncoding))
    Dim sResponse As String = Reader.ReadToEnd()

    'close handles
    Reader.Close()
    Response.Close()
  End Function
End Class