Hard to diagnose exception thrown when AzureADOptions.Instance is not set

[DamianEdwards]

I was migrating an app that uses Azure AD auth from 1.x to 2.1, including using the new UI package. I had not set AzureADOptions.Instance (as this is new in 2.x and I didn't know it needed to be set). The exception that results does not have user-code on the stack, and thus has no line numbers. The exception is from the Uri constructor, which is being passed a null string (from this line).

We should ensure we validate options properties before using them to create other types where they might throw, as it's incredibly hard for app devs to diagnose.

@javiercn @blowdart

[muratg]

@danroth27 @mkArtakMSFT is @javiercn the owner for this? Is is to be done in Preview3 or at a later preview?

[danroth27]

@blowdart

[blowdart]

When did that happen? It's not identity. When you're back then I need a break down of what the goals were for this feature.

[javiercn]

We can validate the options here using "options validation" or just throw an exception, it shouldn't be very costly, but it's very low on priority IMO

[analogrelay]

We should just check the Instance for null-or-empty and throw a useful exception.