Cloud Developer: Office 365 REST API returns 401 access denied with an error code of “invalid_token”

In recent times i worked with this cloud developer (Azure AD, Office 365 REST API) where they created a custom application. It uses (Calendar, Contact, Mail APIs) to pull items from the specified user mailbox. Intermittently they see “401 Access Denied” followed by error code “invalid_token” from the API. During the investigation, we noticed that…

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