I am trying to send emails through gmail host by using google oauth 2.0, where to use the access code instead of user password to send emails

I am trying to send emails through gmail host by using google oauth 2.0, I am confused where to use the access code instead of user password to send emails,

this code is used to open up the consent screen and ask for permissions,

    Dim Googleurl = "https://accounts.google.com/o/oauth2/auth?response_type=code&redirect_uri=" & googleplus_redirect_url & "&scope=https://www.googleapis.com/auth/userinfo.email%20https://www.googleapis.com/auth/userinfo.profile%20https://mail.google.com/%20https://www.googleapis.com/auth/gmail.send&client_id=" + googleplus_client_id
    Session("loginWith") = "google"
    Response.Redirect(Googleurl)

after getting permissions, this is how I obtained access code,

                If url <> "" Then
                    Dim queryString As String = url.ToString()
                    Dim delimiterChars As Char() = {"="c}
                    Dim words As String() = queryString.Split(delimiterChars)
                    Dim code As String = words(1)

                    If code IsNot Nothing Then
                        Dim webRequest As HttpWebRequest = CType(webRequest.Create("https://accounts.google.com/o/oauth2/token"), HttpWebRequest)
                        webRequest.Method = "POST"
                        Parameters = "code=" & code & "&client_id=" & googleplus_client_id & "&client_secret=" + googleplus_client_secret & "&redirect_uri=" + googleplus_redirect_url & "&grant_type=authorization_code"
                        Dim byteArray As Byte() = Encoding.UTF8.GetBytes(Parameters)
                        webRequest.ContentType = "application/x-www-form-urlencoded"
                        webRequest.ContentLength = byteArray.Length
                        Dim postStream As Stream = webRequest.GetRequestStream()
                        postStream.Write(byteArray, 0, byteArray.Length)
                        postStream.Close()
                        Dim response As WebResponse = webRequest.GetResponse()
                        postStream = response.GetResponseStream()
                        Dim reader As StreamReader = New StreamReader(postStream)
                        Dim responseFromServer As String = reader.ReadToEnd()
                        Dim serStatus As GooglePlusAccessToken = JsonConvert.DeserializeObject(Of GooglePlusAccessToken)(responseFromServer)
                        If serStatus IsNot Nothing Then
                            Dim accessToken As String = String.Empty
                            accessToken = serStatus.access_token

                            If Not String.IsNullOrEmpty(accessToken) Then
                                getgoogleplususerdataSer(accessToken)
                            End If
                        End If
                    End If
                End If

and using the below code to send emails:

                        mm.Subject = LetterSubject.Text
                        Dim body As String
                        body = LetterBody.Text
                            mm.Body = body
                        Dim smtp As New Mail.SmtpClient()
                        smtp.Host = "smtp.gmail.com"
                        smtp.EnableSsl = True
                        smtp.Port = 587
                        smtp.UseDefaultCredentials = False
                        Dim service = New GmailService(New BaseClientService.Initializer With {.HttpClientInitializer = cred})
                        Dim NetworkCred As New NetworkCredential(SenderEmailAddress.Text, SenderPassword.Text)
                        smtp.Credentials = NetworkCred
                        smtp.Send(mm)

Can someone please help me how to use token here to send emails without using the user gmail password?

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