I have 02 custom web api. One using user and password and another using Azure AD App Only token to connect to SharePoint Online. None of them are performing batch activities, but simple CRUD activities.
However sometimes the custom WEB Api, using user and password, got throttled, recieving a 503 "Server too busy" response from SharePoint Online.
I'm planning to change that authentication to Azure AD App Only token, because I never receive that reponse when using Azure AD App Only token. Or maybe it's something related to the amount of resource quota assigned to the site collection.
- Custome Web API using user and password is deployed on premise server.
- Custome Web API using Azure AD App Only token is deployed on an App Service in Azure.