Over the past couple of weeks I’ve been assisting with the development work of an enterprise system that uses both Azure Active Directory (Azure AD) and Google to authenticate users. It’s a cross platform solution which means we need code that works across both authentication platforms, and the three mobile platforms. Unfortunately this is easier said than done – The Azure AD team have done a reasonable job with the ADAL library but it’s not like we can repurpose that library for authenticating against Google. This is a tad annoying since both Azure AD and Google both use OAuth and OpenID Connect, so you’d expect there to be a good library that would work across both.
In trying to find a workable solution I can across a number of links that I want to bookmark here for future reference:
Home - https://oauth.net/2/
The OAuth home page is a good starting point if you want to get more links and information about OAuth (1 and 2) but I actually found it’s main use for me was to point at the OAuth 2.0 Framework RFC
OAuth 2.0 Framework RFC - https://tools.ietf.org/html/rfc6749
You can think of the OAuth 2.0 Framework RFC as being the specification for OAuth 2.0. There are some extensions and other standards that relate to OAuth 2.0 but this is a must read if you want to understand what OAuth 2.0 is all about. You may need to refer back to this when reading other blogs/tutorials as it can help clarify what each of the roles and responsibilities are in the process.
Simple overview of OAuth 2 - https://aaronparecki.com/2012/07/29/2/oauth2-simplified
This overview provides a quick summary of the various flows for OAuth 2.0. However, I disagree with the use of the implicit workflow for mobile applications. Whilst mobile applications are not “trusted,” which would normally imply the use of the implicit workflow, the reality is that the implicit workflow can’t issue refresh tokens. This means that unless you want your users to have to log in each time they use your mobile application, you need to use the Authorization Code workflow (the client secret shouldn’t be required when requesting access tokens for mobile apps – this depends on which authentication provider you’re using).
Home - http://openid.net/connect/
The OpenID Connect home page is again a good starting point as it links to the many different parts of the OpenID Connect standard. OpenID Connect builds on top of OAuth 2.0 in order to provide a mechanism for users to be authenticated as well as authorized for resource access. In addition to the creation of access tokens, OpenID Connect defines an id_token which can be issued in absence of any resource that is just used to identify the user that has authenticated.
OpenID Connect Core 1.0 - http://openid.net/specs/openid-connect-core-1_0.html
This is the core specification of OpenID Connect. Similar to the specification for OAuth, this is worth both a read and to be used as a reference when working with OpenID Connect implementations.
OpenID Connect Session Management 1.0 - http://openid.net/specs/openid-connect-session-1_0.html
Whilst still in draft this standard covers how implementers are supposed to handle log out scenarios, which is useful as your application can’t simply delete it’s access tokens when a user opts to log out. Ideally when a user logs out, you’d want to make sure both cached tokens are cleared, along with invalidating any access or refresh tokens.
OAuth 2.0 Overview - https://developers.google.com/identity/protocols/OAuth2
OpenID Connect - https://developers.google.com/identity/protocols/OpenIDConnect
Google’s documentation isn’t too bad but does require you to read all of the pages as the OAuth and OpenID Connect implementation details seem to be scattered across the pages. The assumption is that for any given type of application you can simply read the one page – unfortunately, if you want to get an understanding of the Google implementation, you really need to read everything. Authenticating/authorizing with Google is significantly simpler than with Azure AD as there is no notion of linking your application registration with specific permissions to other applications registered with Azure AD. This is a significant limitation of using Google sign in, as you can really only use it to authenticate and then use the token to access various Google APIs.
Azure Active Directory
Azure AD Developer’s Guide - https://docs.microsoft.com/en-au/azure/active-directory/develop/active-directory-developers-guide
Authentication Scenarios for Azure AD - https://docs.microsoft.com/en-au/azure/active-directory/develop/active-directory-authentication-scenarios
Azure AD is a much longer read, and it’s very easy to get lost in the world of application configuration and settings. My recommendation is to start with something simple, and then grow from that. For examples, start by authenticating a use to sign into your mobile app, then extend it so that you can use the access token to connect to a Web API, and then on to retrieve information from other Microsoft services within the Web API, and then perhaps make it all multi-tenanted (that’s one for another post!).