[naasking]

Even linear workflows can handle conditional execution, you just lift the condition into a value, like into a Maybe/Option type, and later stages only execute if there's a value.

Or if you want to be more literal, declare a specific type:

    type Authenticated(User) = No | Yes(User)

And each stage of your workflow matches on Authenticated.Yes, and so only executes if the user is authenticated. That's basically what any system does internally, this just makes that implicit behaviour explicit.