Announcing OAuth 2.0 Client Credentials Flow support for POP and IMAP protocols in Exchange Online

I implement the OAuth 2.0 client credentials grant flow for POP3. It works fine, but only for 1 sometimes 2 or 3 hours an then not any more. The error message is “-ERR Authentication failure: unknown user name or bad password.” That is not plausible for me, because TENET ID, CLIENT ID and CLIENT SECRET are correct. Do you have an Idea what is the cause for this behavior?

After the first authentication failure, I try to obtain a new access token in the same way I obtained the first original one. But it seems that it does not work.

An auto refreshing of the access token can not work, because of the obtained token. There is no property “refresh_token” exist (see below the obtained token as json file).

{

  "token_type": "Bearer",

  "expires_in": 3599,

  "ext_expires_in": 3599,

  "access_token": "eyJ0eXAiOiJKV1QiLCJub25jZSI--XXXXXXXXXX"

}

Without the property “refresh_token” it is not possibel to refresh the access token.

Could you Please help me how to solve this problem.

Thanks!