Hello @Sergio Alberto Gonzalez Quiros , in order to develop a solution that includes a React front-end app and a Java back-end app that creates events in Microsoft 365 you need to review the following resources and samples:
- React single-page application built with MSAL React and Microsoft identity platform: Replace calls to Microsoft Graph with calls to your Java API,
- Java web API written in Spring Boot that calls Microsoft Graph as itself. : Authorizing the API application to Microsoft Graph
- Or
- A Java Web API that calls another web API with the Microsoft identity platform using the On-Behalf-Of flow: Authorizing the signed-in user to Microsoft Graph
- Microsoft Graph API Create event operation with Java sample code
Let us know if you need additional assistance. If the answer was helpful, please accept it and rate it so that others facing a similar issue can easily find a solution.