Dim privateKeyStream As Stream = New FileStream("D:\docusign.pem", FileMode.Open)
'Dim privateKeyStream As Stream = New MemoryStream(Encoding.UTF8.GetBytes(PK))
Using SR = New StreamReader(privateKeyStream)
    If Not SR Is Nothing And SR.Peek() > 0 Then
        Dim privateKeyBytes() As Byte = ReadAsBytes(privateKeyStream)
        'Dim privateKeyBytes() As Byte = StreamToByteArray(privateKeyStream)
        'Dim privateKeyBytes() As Byte = Convert.FromBase64String(PrivateKey)
        'Dim privateKeyBytes() As Byte = Encoding.UTF8.GetBytes(PrivateKey)

        Dim privateKeyS As String = Encoding.UTF8.GetString(privateKeyBytes)

        Dim handler As JwtSecurityTokenHandler = New JwtSecurityTokenHandler()
        handler.SetDefaultTimesOnTokenCreation = False

        Dim descriptor As SecurityTokenDescriptor = New SecurityTokenDescriptor()
        descriptor.Expires = DateTime.UtcNow.AddHours(1)
        descriptor.IssuedAt = DateTime.UtcNow

        Dim scopes As List(Of String) = New List(Of String)
        scopes.Add(OAuth.Scope_SIGNATURE)

        descriptor.Subject = New ClaimsIdentity()
        descriptor.Subject.AddClaim(New Claim("scope", String.Join(" ", scopes)))
        descriptor.Subject.AddClaim(New Claim("aud", "account-d.docusign.com"))
        descriptor.Subject.AddClaim(New Claim("iss", "INTEGRATION_ID"))
        descriptor.Subject.AddClaim(New Claim("sub", "ACCOUNT_ID"))

        Dim RSA = CreateRSAKeyFromPem(privateKeyS)
        Dim rsaKey As RsaSecurityKey = New RsaSecurityKey(RSA)
        descriptor.SigningCredentials = New SigningCredentials(rsaKey, SecurityAlgorithms.RsaSha256Signature)


        Dim Token = handler.CreateToken(descriptor)
        Dim jwtToken As String = handler.WriteToken(Token)

        Dim baseUri As String = String.Format("https://{0}/", basePath)
        Dim RestClient As RestClient = New RestClient(baseUri)
        RestClient.Timeout = 10000

        Dim contentType As String = "application/x-www-form-urlencoded"

        Dim formParams As New Dictionary(Of String, String)
        formParams.Add("grant_type", OAuth.Grant_Type_JWT)
        formParams.Add("assertion", jwtToken)

        Dim queryParams As New Dictionary(Of String, String)

        Dim headerParams As New Dictionary(Of String, String)
        headerParams.Add("Content-Type", "application/x-www-form-urlencoded")
        headerParams.Add("Cache-Control", "no-store")
        headerParams.Add("Pragma", "no-cache")

        Dim fileParams As New Dictionary(Of String, FileParameter)
        Dim pathParams As New Dictionary(Of String, String)

        Dim postBody As Object = Nothing

        Dim request As RestRequest = PrepareRequest(basePath, Method.POST, queryParams, postBody, headerParams, formParams, fileParams, pathParams, contentType)

        Dim response As IRestResponse = RestClient.Execute(request)

        If (response.StatusCode >= HttpStatusCode.OK And response.StatusCode < HttpStatusCode.BadRequest) Then
            Dim tokenInfo As OAuth.OAuthToken = JsonConvert.DeserializeObject(Of OAuth.OAuthToken)(response.Content)
            Return tokenInfo.access_token
        Else
            Throw New ApiException(response.StatusCode, "Error while requesting server, received a non successful HTTP code " & response.ResponseStatus & " with response Body: " + response.Content, response.Content)
        End If
    Else
        Throw New ApiException(400, "Private key stream not supplied or is invalid!")
    End If
End Using