type Options struct {
	// TokenExchangeServiceURI is the address of the server which implements STS
	// token exchange functionality.
	TokenExchangeServiceURI string // Required.

	// Resource is a URI that indicates the target service or resource where the
	// client intends to use the requested security token.
	Resource string // Optional.

	// Audience is the logical name of the target service where the client
	// intends to use the requested security token
	Audience string // Optional.

	// Scope is a list of space-delimited, case-sensitive strings, that allow
	// the client to specify the desired scope of the requested security token
	// in the context of the service or resource where the token will be used.
	// If this field is left unspecified, a default value of
	// https://www.googleapis.com/auth/cloud-platform will be used.
	Scope string // Optional.

	// RequestedTokenType is an identifier, as described in
	// https://tools.ietf.org/html/rfc8693#section-3, that indicates the type of
	// the requested security token.
	RequestedTokenType string // Optional.

	// SubjectTokenPath is a filesystem path which contains the security token
	// that represents the identity of the party on behalf of whom the request
	// is being made.
	SubjectTokenPath string // Required.

	// SubjectTokenType is an identifier, as described in
	// https://tools.ietf.org/html/rfc8693#section-3, that indicates the type of
	// the security token in the "subject_token_path" parameter.
	SubjectTokenType string // Required.

	// ActorTokenPath is a  security token that represents the identity of the
	// acting party.
	ActorTokenPath string // Optional.

	// ActorTokenType is an identifier, as described in
	// https://tools.ietf.org/html/rfc8693#section-3, that indicates the type of
	// the security token in the "actor_token_path" parameter.
	ActorTokenType string // Optional.
}