What version of Docker.DotNet?:

fork from main as of 2/14/2021 (commit 8e3cf4f)

Problem:
ISystemOperations.AuthenticateAsync does not provide a way for the caller to get the token that was returned in the REST response.

Its signature is Task AuthenticateAsync(AuthConfig authConfig, CancellationToken cancellationToken = default(CancellationToken)), but it should probably be Task<AuthResponse> AuthenticateAsync(AuthConfig authConfig, CancellationToken cancellationToken = default(CancellationToken)) instead.

Other details:
I'm happy to submit a PR, but what's this project's preferred way to handle changes that would break binary compatibility? Just changing the return type would be breaking. An overload with an out parameter isn't possible because it's an async method. Are you OK with adding an Authenticate2Async method or similar?