Using Nautdrafter there are two options for logging in: As a player through Steam or as an anonymous spectator.
Logging in as a Player
Click the "Login as player" button
Depending on if you are logged into Steam, this will either take you through to the next screen or open your default browser and display the Steam login.
If you had not logged into Steam, once you have finished logging in through your browser, Nautdrafter should have automatically been notified and will take you to the next screen.
Joining as a Spectator
Click the "Continue as spectator" button
No Steam account is required and Nautdrafter should display the next screen.
Login uses Steam Web API and OpenID.