Support for Multi-Tenancy

[rdbartram]

Since graph binding forces you to set the issuerURL in the AD Application that is assigned to the function, I am unable to find a way to support multitenancy.

Want I want is that any user from any tenant can call the api and be authenticated against their own Azure AD using delegated permissions. I have it working if I make the calls myself to get the token, but it would be nice if the binding could use the same issuer that was used to issue the authenticated user.

Perhaps i'm missing something, if so just tell me :D