client

type IDer interface {
	// ID returns the client ID as typically defined in a service
	// account token.
	ID(context.Context) (string, error)
}

type Interface interface {
	IDer
	WithHeaderer
}

type Options struct {
	// IDHeader is the header key used when building a request
	// via Interface.WithHeader.
	IDHeader string

	// TokenPath is the file path from which the client ID will be
	// read via Interface.ID.
	TokenPath string

	// TokenExpiry defines the expected expiry time of the token
	// read from TokenPath. A TokenExpiry value that is less than
	// zero will build a long lived token reader that caches the
	// token value indefinitely.
	TokenExpiry time.Duration
}

type WithHeaderer interface {
	// WithHeader returns a clone of the given request that
	// includes the client ID set as the value of the configured
	// header.
	WithHeader(*http.Request) (*http.Request, error)
}