You are calling the constructor of the OptionsMonitor<TOptions>
class incorrectly.
In this case I would have just mocked the IOptionsMonitor<AuthenticationSettings>
interface
For example using Moq
AuthenticationSettings au = new AuthenticationSettings() { ... };
var monitor = Mock.Of<IOptionsMonitor<AuthenticationSettings>>(_ => _.CurrentValue == au);
ActiveDirectoryLogic _SUT = new ActiveDirectoryLogic(monitor);