Phase out use of default region
The other SDKs have phased out using the default region returned by the identity service due to legal reasons. The .NET SDK should follow suit and require that a user either specify the region in the provider constructor, on the method call or must be using a global endpoint.
The SDK already does not have a default region. One of the ways a user can explicitly specify a region is by setting metadata at the account level. Following authentication, if the authentication response for a specific account explicitly specifies the region to use in cases where the code did not specify the region, the SDK can use this value. This pattern should already adhere to the legal requirement of placing region specification in the hands of users; changing the code would be a breaking change for some applications that is unlikely to provide users with benefits.
I just confirmed that the other SDKs removed relying upon the account level default due to legal. Keeping issue open.