Hi Mathias,
Single sign-on provides users with the ability to use their corporate credentials to get single sign-on (SSO) to cloud services such as those in Microsoft Office 365 for enterprises. You can get more information about how single sign-on works in Office 365 via the following link:
community.office365.com/.../727.aspx
Meanwhile, in SharePoint Online for Microsoft Office 365 for enterprises, you can use the Business Connectivity Services (BCS) application to present external data coming from Windows Communication Foundation (WCF) web services to your users. For more information, please refer to the link below:
office.microsoft.com/.../manage-business-connectivity-service-applications-HA102677933.aspx
Thanks,
Nancy Xie