Setup OAuth 2.0 Client

1. Register Microsoft OAuth App. More info on this here https://docs.microsoft.com/en-us/azure/active-directory/develop/quickstart-register-app. Choose Accounts in any organizational directory (Any Azure AD directory - Multitenant) and personal Microsoft accounts (e.g. Skype, Xbox) as Supported Account Type option. Copy Application (client) ID (CLIENT_ID) value.
2. Configure platform settings for the app, choose "Web" as the platform type. Add a redirect uri. You should be able to verify ownership of this domain in order publish to production.
3. Create a new client secret for the application. Copy the secret value(CLIENT_SECRET) as this will be needed in a later step.
4. Configure permissions Calendars.Read API permission.

Implement OAuth 2.0 Authorization Code Flow

https://learn.microsoft.com/en-us/azure/active-directory/develop/v2-oauth2-auth-code-flow#redeem-a-code-for-an-access-token

Code samples from Calendar V2 Demo Repository:

• https://github.com/recallai/calendar-integration-demo/blob/v2/v2-demo/logic/oauth.js#L21
• https://github.com/recallai/calendar-integration-demo/blob/v2/v2-demo/routes/oauth-callback/microsoft-outlook.js#L27