Choosing the OAuth2 grant flow

The OAuth2 specifications define six different grant types ( and Each provides the most optimal (from the security point of view) way of obtaining access or (for OIDC) id_tokens given the circumstances of the client application. This blog summarizes the questions that the implementer of the OAuth2 client application needs to ask and how […]

Federation patterns using Azure AD

Objectives This post considers scenarios where an application needs to be accessed by users from many sources of authentication. (Office 365, owned and operated by Microsoft but whose use is managed separately by many independent organizations is an example of such a resource). It proposes a framework for determining an optimal solution for the application […]

Developing an Azure AD B2C multi-tenant application

The ‘regular’ Azure AD has build-in support for multi-tenant applications. In that case, a user from any Azure AD tenant can sign in to an application registered in another tenant. The application can then use the user’s security context to give the user a view of data that is specific to that tenant. The goal […]

Claims augmentation with OWIN but outside of Startup code

Claims list included in the ClaimsPrincipal usually originate from the security token received by the application as part of user authentication (SAML, OpenIDConnect id token) or access authorization (OAuth2 bearer access token).  However, sometimes there is a need to modify that list with claims derived from other sources: Attributes retrieved from custom databases Attributes not initially included […]

Using Azure AD to enable partner access to SharePoint 201x

Introduction The following summarizes my experience with setting Azure AD as authentication provider for Sharepoint 2013 or 2016. This setup enables access to SharePoint for external users (business partners, customers). While there are other approaches that could be used for this purpose, e.g. an on-premises AD with ADFS, using Azure AD has a number of advantages: No […]

Discovering AuthorizeAttribute role names

The AuthorizeAttribute is used in ASP.NET code to decorate controller classes and methods which require authorization, e.g. [Authorize(Roles =“admin”)] public class HomeController : Controller { Meaning that to call any method in this class, the user needs to have a role claim with the value ‘admin’. With many controllers and methods the number of roles used […]