Fix | Fixes concurrent connection speed issues due to 'Authentication Context' cache not maintained in NetCore

[David-Engel]

The authentication context cache of the connection pool was not being updated upon successful fedauth authentication in the netcore code. This was resulting in poor connection speed for subsequent connections which used AAD auth since they could not take advantage of the cached token. This code looks to have been missed when AAD authentication was ported from netfx to netcore.

This was found during investigation of #408

The new test should detect if subsequent connections are not using the cache. Hopefully connection times are consistent enough that this does not produce intermittent failures.

[Wraith2]

It might be worth using private reflection to reach into the internals and find the cache to verify that it has been populated rather than relying on a timing artefact that could be flaky. I know private reflection is generally bad but as the owners you're allowed to assume your own internal details in this case I'd say.

[David-Engel]

It might be worth using private reflection to reach into the internals and find the cache to verify that it has been populated rather than relying on a timing artefact that could be flaky. I know private reflection is generally bad but as the owners you're allowed to assume your own internal details in this case I'd say.

@Wraith2
I expect _dbConnectionPool.AuthenticationContexts.Count > 0 in SqlInternalConnectionTds after the first connection. I spent some time trying to wind my way through to view that via Reflection, but it was not apparent to me how to get to it. I'll have to revisit it later if I find the time. (If you have some time to spare, you're probably quicker than I am. 😁)