lib3.go

package mylib

import "net/http"

// New create a new Instance of mylib
func New(someAlwaysRequiredValue string, options ...func(*Instance) error) (*Instance, error) {
	return &Instance{
		client: new(http.Client), // default no auth client
	}, nil
}

type Instance struct {
	client *http.Client
}

// BasicAuth creates a function that sets the username and password for requests when passed as an options function.
func BasicAuth(username, password string) func(*Instance) error{
	return func(i *Instance) error {
		// create an http client where the basic credentials
		// are injected automatically into requests.
		client,err := //...
		if err != nil {
			return err
		}
		i.client = client
		return nil
	}
}

// OAuth ...
func OAuth(id, secret string) func(*Instance) error{
	// ....
	return func(i *Instance) error {
		return nil
	}
}