Add support for fmt.Stringer implementations in Go SDK Oso methods, or propagate a warning message in instances where a type defined string is passed as the action argument

[nathan-fiscaletti]

Methods such as the Authorize(actor interface{}, action interface{}, resource interface{}) method only accept direct string types as a value for the action parameter.

A common implementation of Oso is to create an enum defining available actions using a custom Action type. A very basic implementation of this might look something like this:

type Action string

const (
     Action_LoginMobile Action = "login_mobile"
     Action_LoginWeb    Action = "login_web"
)

func (a Action) String() string {
    return string(a)
}

However, if you pass one of these constants into the Authorize function, it will not properly detect whether or not the action is authorized. This is because the Authorize() function expects a string, not a custom type.

There is also no log message, warning or error indicating the mistake.

---

One possible solution to this would be to update the Authorize function to accept an implementation of the fmt.Stringer interface.

This might look something like this:

func Authorize(actor, action, resource interface{}) error {
	var actionStr string
	switch v := action.(type) {
	case string:
		actionStr = v
	case fmt.Stringer:
		actionStr = v.String()
	default:
		return fmt.Errorf("action must be either a valid string or implement the fmt.Stringer interface")
	}

	fmt.Printf("found action: %v\n", actionStr)
	return nil
}

. . .

err := Authorize(user, Action_LoginMobile, resource)

Alternately, simply providing an error or a warning indicating that the Authorization will fail due to an incorrect type being passed to the method would at least inform the caller that they need to be passing a string type, and not a type definition that resolves to a string.