The code below deadlocks o365rwsclient when invoked from a GUI app (such as a Windows Forms app) or an MVC appllication.

            ReportingContext context = new ReportingContext();
            context.UserName = @"YOUR O365 EMAIL ADDRESS";
            context.Password = @"YOUR O365 PASSWORD";
            context.FromDateTime = DateTime.MinValue;
            context.ToDateTime = DateTime.MinValue;
            context.SetLogger(new DefaultLogger());

            IReportVisitor visitor = new DefaultReportVisitor();

            ReportingStream stream = new ReportingStream(context, "MailboxActivityDaily", "stream1");
            stream.RetrieveData();

The reason is that RetrieveData eventually calls GetResponseXml. The method
public List<XmlNode> GetResponseXml(Type reportType, QueryFilter filter) has the line
Stream responseContent = GetResponseContentAsync(serviceFullUrl).Result;

Blocking on the results of asynchronous methods is dangerous: see, for example,
http://blog.stephencleary.com/2012/07/dont-block-on-async-code.html

A possible fix is to configure the awaits in GetResponseContentAsync to not capture context using ConfigureAwait(false).

Ideally all methods making I/O calls should be marked with the async keyword and return a Task. This is important for the client classes as well as the contracts like ITraceLogger and IReportVisitor which will likely require making an async call in their implementation.

Is there any form for using it in form applications?

partner and scorecard reports don't have TenantName property, and it's unclear whether they should inherit TenantReportObject class.

The o365 Modular Input for Splunk invokes O365 using this library. It requires a user to provide credentials as well as a report name. Validation doesn't appear to happen until you attempt to Stream. It would be nice to have a simple validation method that can verify whether or not the credentials / report is valid without having to stream.

Perhaps there is a way to do this and it is just not obvious (to me).

Change Password type from string to securestring
ReportingContext context = new ReportingContext();
context.UserName = @"YOUR O365 EMAIL ADDRESS";
context.Password = @"YOUR O365 PASSWORD";

Mail reports cannot inherit TenantReportObject class, as they don't have TenantGuid and TenantName. New base class should be created.