As Diederik says, the general purpose API to talk to REST services from UWP is HttpClient. See https://docs.microsoft.com/en-us/windows/uwp/networking/httpclient and https://github.com/Microsoft/Windows-universal-samples/tree/master/Samples/HttpClient
For general oAuth authentication use the WebAuthenticationBroker. See https://docs.microsoft.com/en-us/uwp/api/Windows.Security.Authentication.Web.WebAuthenticationBroker and https://github.com/Microsoft/Windows-universal-samples/tree/master/Samples/WebAuthenticationBroker
For specific services you'll want to check in the appropriate documentation or forums for those services. They may also provide high level SDKs that wrap the REST calls.
OneDrive docs: https://developer.microsoft.com/en-us/onedrive
OneDrive discussion: see links in Support menu at https://developer.microsoft.com/en-us/onedrive
Graph API docs: https://developer.microsoft.com/en-us/graph
Graph API forum: https://social.msdn.microsoft.com/Forums/en-US/home?forum=WindowsAzureAD
OneDrive login with Graph: https://docs.microsoft.com/en-us/onedrive/developer/rest-api/getting-started/graph-oauth
Azure ActiveAD Authentication Library: https://github.com/AzureAD/azure-activedirectory-library-for-dotnet
Microsoft Authentication Library (MSAL) Preview for .NET https://aka.ms/aaddev
