Consuming Rest APIs of O365/SharePoint Online

Question

I need to get the data via rest api from SharePoint list and Outlook calendar. We have out of the box end points to get the data from browser after logging into O365. But i my case, i have a mobile application where i needs to display my data. Is any token or ids needed?. How can i request data from a 3rd party app. assume SSO is enabled or that app will supply the credentials.

 

Kinldy let me know if anyone have a hint/ suggestion for this scenario. 

 

Thanks.