Add a helper extension for setting up authentication with Azure AD

[danroth27]

We should provide some extensions that simplify setting up authentication with Azure AD for both web apps and web APIs. Here is what the templates current do:

https://github.com/dotnet/templating/tree/rel/vs2017/3-Preview2/template_feed/Microsoft.DotNet.Web.ProjectTemplates.2.0/content/StarterWeb-CSharp/Extensions/AzureAd

https://github.com/dotnet/templating/tree/rel/vs2017/3-Preview2/template_feed/Microsoft.DotNet.Web.ProjectTemplates.2.0/content/WebApi-CSharp/Extensions/AzureAd

See also #1213 and #1212

[danroth27]

@vibronet

[kevinchalet]

Pretty much what I suggested in November when the AzureAD-specific/non-standard telemetry stuff was added directly in IdentityModel:

#1035 (comment)
#1035 (comment)

[Tratcher]

@danroth27 AzureAdOpenIdConnectOptionsSetup has code that looks intended to be customized.

[HaoK]

Well customers can just tweak the resulting options with a normal services.Configure<OpenIdConnectOptions> instead of editing the setup class too

[danroth27]

Right, all the places where we want to point customers to customize the code we would recreate in the template using a call to services.Configure<OpenIdConnectOptions>

[danroth27]

@ajcvickers @Eilon @muratg

@HaoK I believe this should be assigned to you, correct? Are you going to be able to get to this by EOW?

[kevinchalet]

@danroth27 now that Azure AD is going to have its own OIDC extension/wrapper, is moving the non-standard/implementation-specific "telemetry" stuff from IdentityModel to this new helper something you could consider?

[danroth27]

@vibronet @Tratcher @brentschmaltz

@PinpointTownes I'm not familiar with the "telemetry" stuff you're referring to. Adding some folks who probably have more context.

[kevinchalet]

@danroth27 here's the feature in question: https://github.com/AzureAD/azure-activedirectory-identitymodel-extensions-for-dotnet/pull/529/files

It was discussed here: #1035.

[HaoK]

@danroth27 now that we are down to 2-3 files, are we ok with this living in the template for preview 2? The AzureAd/B2C Options concept is just a template concern, and the OptionsInitialize (which we'll need to rename to PostConfigure once the Options PR is in), is pretty simple (sets authority using the Azure options). And you wanted the other events code in the template anyways