There are a lot of arguments for and against using pre-built SDKs for doing OAuth authentication with Azure AD and Google. Having worked with the ADAL library for Azure quite a bit I think the team have done a reasonable job, especially considering it now works across the three mobile platforms (iOS, Android and Windows), and works with a PCL that is .NET Standard based. However, using any library does force you into working within the bounds of the library. For example, we recently found two shortcomings in the library:
– It doesn’t provide a good solution for doing a browser based workflow for signing in – instead it uses a webview hosted within the context of the application (depending on the platform this may be augmented with more security, for example the Web Authentication Broker – https://msdn.microsoft.com/en-us/library/windows/apps/windows.security.authentication.web.webauthenticationbroker.aspx). A browser based workflow involves launching the external browser for the user to sign in; upon successful sign on, the user is redirected back to the app.
– It doesn’t provide a mechanism to clear cached credentials. Whilst the tokens can be cleared, this doesn’t clear the cookies held within the hosted webview, which can lead to issues if the application is multi-tenanted.
If the provided libraries don’t align with what you want, you may have to roll your own solution. The Authorization Code workflow requires two endpoints:
– Authorize URL – this is the URL that you navigate the user to in order for them to sign into your application. After signing in an Authorization Code is returned to the application
– Token URL – this is the URL that the application does a POST request to in order to convert the Authorization Code into an access token.
For Azure Active Directory, these endpoints are:
For Google, these endpoints are:
Authorize – https://accounts.google.com/o/oauth2/v2/auth
As both services conform to OAuth/OpenID Connect, the parameters are the same, although there are some variations on the values that you need to supply for scope and client id.