(Visual FoxPro) Auto-Refresh O365 Access Token when Sending Email

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Demonstrates how to automatically recover from an expired access token when sending email from smtp.office365.com using OAuth2 authentication. If the server responds with an error indicating that the access token is expired, then we refresh the access token and retry.

Chilkat ActiveX Downloads ActiveX for 32-bit and 64-bit Windows

LOCAL loJsonToken
LOCAL lnSuccess
LOCAL loMailman
LOCAL loEmail
LOCAL loOauth2
LOCAL loSbJson

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

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

* First get our previously obtained OAuth2 access token.
* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.JsonObject')
loJsonToken = CreateObject('Chilkat.JsonObject')
lnSuccess = loJsonToken.LoadFile("qa_data/tokens/office365.json")

* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.MailMan')
loMailman = CreateObject('Chilkat.MailMan')

loMailman.SmtpHost = "smtp.office365.com"
loMailman.SmtpPort = 587
loMailman.StartTLS = 1

* Use your Office365 email address for the SmtpUsername.
loMailman.SmtpUsername = "OFFICE365_EMAIL_ADDRESS"
loMailman.OAuth2AccessToken = loJsonToken.StringOf("access_token")

* Create a new email object
* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.Email')
loEmail = CreateObject('Chilkat.Email')

loEmail.Subject = "This is a test"
loEmail.Body = "This is a test"
loEmail.From = "MY_NAME <OFFICE365_EMAIL_ADDRESS>"
lnSuccess = loEmail.AddTo("John Doe","somebody@example.com")

* Call SendEmail to connect to the SMTP server and send.
* The connection (i.e. session) to the SMTP server remains
* open so that subsequent SendEmail calls may use the
* same connection.  
lnSuccess = loMailman.SendEmail(loEmail)
IF (lnSuccess = 1) THEN
    ? "Mail Sent!"
    RELEASE loJsonToken
    RELEASE loMailman
    RELEASE loEmail
    CANCEL
ENDIF

* If we fall through to here, it means something failed.
* If we failed because of an invalid or expired access token, we should get this SMTP status code and error message:
*    response: 535 5.7.3 Authentication unsuccessful [CH2PR19CA0023.namprd19.prod.outlook.com]
*    status code: 535
IF (loMailman.LastSmtpStatus <> 535) THEN
    ? loMailman.LastErrorText
    RELEASE loJsonToken
    RELEASE loMailman
    RELEASE loEmail
    CANCEL
ENDIF

* If we get here, it means the SMTP status code equaled 535, which is an authentication failure.
* Let's refresh the access token, and then retry..

* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.OAuth2')
loOauth2 = CreateObject('Chilkat.OAuth2')

* Update to use your token endpoint.
* In the Azure Portal, in "App registrations", go to "Endpoints" (located to the right of the "+ New registration" link.)
*    Find your endpoint for the "OAuth 2.0 token endpoint (v2)"
*    See Office365 OAuth2 Endpoints

loOauth2.TokenEndpoint = "https://login.microsoftonline.com/xxxxxxxxxx-71bf-4ebe-a866-738364321bf2/oauth2/v2.0/token"

* Replace these with actual values.
loOauth2.ClientId = "CLIENT_ID"
loOauth2.ClientSecret = "CLIENT_SECRET"

* Get the "refresh_token"
loOauth2.RefreshToken = loJsonToken.StringOf("refresh_token")

* Send the HTTP POST to refresh the access token..
lnSuccess = loOauth2.RefreshAccessToken()
IF (lnSuccess <> 1) THEN
    ? loOauth2.LastErrorText
    RELEASE loJsonToken
    RELEASE loMailman
    RELEASE loEmail
    RELEASE loOauth2
    CANCEL
ENDIF

? "New access token: " + loOauth2.AccessToken
? "New refresh token: " + loOauth2.RefreshToken

* Update the JSON with the new tokens.
loJsonToken.UpdateString("access_token",loOauth2.AccessToken)
loJsonToken.UpdateString("refresh_token",loOauth2.RefreshToken)

* Save the new JSON access token response to a file.
* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.StringBuilder')
loSbJson = CreateObject('Chilkat.StringBuilder')
loJsonToken.EmitCompact = 0
loJsonToken.EmitSb(loSbJson)
loSbJson.WriteFile("qa_data/tokens/office365.json","utf-8",0)

? "OAuth2 authorization granted!"
? "New Access Token = " + loOauth2.AccessToken

* -------------------------------------------------
* Retry the SMTP send using the refreshed access token.

? "Retrying the send using the refreshed access token."

loMailman.OAuth2AccessToken = loOauth2.AccessToken

lnSuccess = loMailman.SendEmail(loEmail)
IF (lnSuccess = 0) THEN
    ? loMailman.LastErrorText
    RELEASE loJsonToken
    RELEASE loMailman
    RELEASE loEmail
    RELEASE loOauth2
    RELEASE loSbJson
    CANCEL
ENDIF

lnSuccess = loMailman.CloseSmtpConnection()
IF (lnSuccess <> 1) THEN
    ? "Connection to SMTP server not closed cleanly."
ENDIF

? "Email sent!"

RELEASE loJsonToken
RELEASE loMailman
RELEASE loEmail
RELEASE loOauth2
RELEASE loSbJson