(VB.NET) POP3 Auto-Refresh Office365 Access Token

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Demonstrates how to automatically recover from an expired OAuth2 access token when OAuth2 authentication fails in the POP3 protocol. If the server responds with "-ERR Authentication failure: unknown user name or bad password.", then we refresh the access token and retry.

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' This example requires the Chilkat API to have been previously unlocked.
' See Global Unlock Sample for sample code.

Dim mailman As New Chilkat.MailMan

mailman.MailHost = "outlook.office365.com"
mailman.MailPort = 995
mailman.PopSsl = True

' Use your O365 email address here.
mailman.PopUsername = "OFFICE365_EMAIL_ADDRESS"

' When using OAuth2 authentication, leave the password empty.
mailman.PopPassword = ""

' Load our previously obtained OAuth2 access token.
Dim jsonToken As New Chilkat.JsonObject
Dim success As Boolean = jsonToken.LoadFile("qa_data/tokens/office365.json")
If (success = False) Then
    Debug.WriteLine(jsonToken.LastErrorText)
    Exit Sub
End If


mailman.OAuth2AccessToken = jsonToken.StringOf("access_token")

' Make the TLS connection to the outlook.office365.com POP3 server.
success = mailman.Pop3Connect()
If (success <> True) Then
    Debug.WriteLine(mailman.LastErrorText)
    Exit Sub
End If


' Authenticate using XOAUTH2
success = mailman.Pop3Authenticate()
If (success <> True) Then
    ' If we're still connected to the mail server, then it means the server sent a non-success response,
    ' Such as:  -ERR Authentication failure: unknown user name or bad password.
    If (mailman.IsPop3Connected = True) Then

        ' Refresh the OAuth2 access token, and if successful, save the new (refreshed) access token and try authenticating again.
        Dim oauth2 As New Chilkat.OAuth2

        ' Use your actual Directory (tenant) ID instead of "112d7ed6-71bf-4eba-a866-738364321bfc"
        oauth2.TokenEndpoint = "https://login.microsoftonline.com/112d7ed6-71bf-4eba-a866-738364321bfc/oauth2/v2.0/token"

        ' Replace these with your Azure App Registration's actual values.
        oauth2.ClientId = "CLIENT_ID"
        oauth2.ClientSecret = "CLIENT_SECRET"

        ' Get the "refresh_token"
        oauth2.RefreshToken = jsonToken.StringOf("refresh_token")

        ' Send the HTTP POST to refresh the access token..
        success = oauth2.RefreshAccessToken()
        If (success <> True) Then
            Debug.WriteLine(oauth2.LastErrorText)
            Exit Sub
        End If


        Debug.WriteLine("New access token: " & oauth2.AccessToken)
        Debug.WriteLine("New refresh token: " & oauth2.RefreshToken)

        ' Update the JSON with the new tokens.
        jsonToken.UpdateString("access_token",oauth2.AccessToken)
        jsonToken.UpdateString("refresh_token",oauth2.RefreshToken)

        ' Save the new JSON access token response to a file.
        Dim sbJson As New Chilkat.StringBuilder
        jsonToken.EmitCompact = False
        jsonToken.EmitSb(sbJson)
        sbJson.WriteFile("qa_data/tokens/office365.json","utf-8",False)

        Debug.WriteLine("New Access Token = " & oauth2.AccessToken)

        ' Update the mailman with the new access token.
        mailman.OAuth2AccessToken = oauth2.AccessToken

        ' Retry the authentication.
        success = mailman.Pop3Authenticate()
        If (success = False) Then
            Debug.WriteLine(mailman.LastErrorText)
            Exit Sub
        End If


    Else
        Debug.WriteLine(mailman.LastErrorText)
        Exit Sub
    End If

End If


' Find out how many emails are on the server..
Dim numEmails As Integer = mailman.CheckMail()
If (numEmails < 0) Then
    Debug.WriteLine(mailman.LastErrorText)
    Exit Sub
End If


' Examine the POP3 session log:
Debug.WriteLine(mailman.Pop3SessionLog)

' The POP3 session log will look something like this:

' **** Connected to outlook.office365.com:995
' < +OK The Microsoft Exchange POP3 service is ready. [QwBIADIAUABSADEANgBDAEEAMAAwADEAMgAuAG4AYQBtAHAAcgBkADEANgAuAHAAcgBvAGQALgBvAHUAdABsAG8AbwBrAC4AYwBvAG0A]
' > AUTH XOAUTH2
' < + 
' > <base64 string in XOAUTH2 format>
' < -ERR Authentication failure: unknown user name or bad password.
' > AUTH XOAUTH2
' < + 
' > <base64 string in XOAUTH2 format>
' < +OK User successfully authenticated.
' > STAT
' < +OK 248 46637086


' End the POP3 session and close the connection to the GMail server.
success = mailman.Pop3EndSession()
If (success <> True) Then
    Debug.WriteLine(mailman.LastErrorText)
    Exit Sub
End If


Debug.WriteLine("Finished.")