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.