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

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Demonstrates how to automatically recover from an expired access token when OAuth2 authentication fails in the IMAP protocol. If the server responds with "NO AUTHENTICATE failed.", then we refresh the access token and retry.

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' An Office365 OAuth2 access token must first be obtained prior
' to running this code.

' Getting the OAuth2 access token for the 1st time requires the O365 account owner's 
' interactive authorizaition via a web browser.  Afterwards, the access token
' can be repeatedly refreshed automatically.

' See the following examples for getting and refreshing an OAuth2 access token

' Get Office365 SMTP/IMAP/POP3 OAuth2 Access Token
' Refresh Office365 SMTP/IMAP/POP3 OAuth2 Access Token

' First get 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("Failed to open the office365 OAuth JSON file.")
    Exit Sub
End If


Dim imap As New Chilkat.Imap

imap.Ssl = True
imap.Port = 993

' Connect to the Office365 IMAP server.
success = imap.Connect("outlook.office365.com")
If (success <> True) Then
    Debug.WriteLine(imap.LastErrorText)
    Exit Sub
End If


' Use OAuth2 authentication.
imap.AuthMethod = "XOAUTH2"

' Login using our username (i.e. email address) and the access token for the password.
success = imap.Login("OFFICE365_EMAIL_ADDRESS",jsonToken.StringOf("access_token"))
If (success <> True) Then
    Dim loginLastErrorText As String = imap.LastErrorText

    ' If we're still connected to the mail server, then it means the server sent a non-success response,
    ' Such as:  NO AUTHENTICATE failed.
    If (imap.IsConnected() = 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)

        ' Retry the login.
        success = imap.Login("OFFICE365_EMAIL_ADDRESS",jsonToken.StringOf("access_token"))
        If (success = False) Then
            Debug.WriteLine(imap.LastErrorText)
            Exit Sub
        End If


    Else
        ' Show the last error text for the call to Login
        Debug.WriteLine(loginLastErrorText)
        Exit Sub
    End If

Else
    Debug.WriteLine("O365 OAuth authentication is successful.")
End If


' Do something...
success = imap.SelectMailbox("Inbox")
If (success <> True) Then
    Debug.WriteLine(imap.LastErrorText)
    Exit Sub
End If


' Your application can continue to do other things in the IMAP session....

' When finished, logout and close the connection.
success = imap.Logout()
success = imap.Disconnect()

Debug.WriteLine("Finished.")