Added authentication method for default directory login

[cocojoe]

Changes

Added support for password grant and authentication with default directory

Method Added

func loginDefaultDirectory(withUsername username: String, password: String, audience: String? = nil, scope: String? = nil, parameters: [String: Any]? = nil)

References

ESD-1363

See: https://auth0.com/docs/api/authentication#resource-owner-password

Testing

• This change adds unit test coverage
• This change has been tested on the latest version of the platform/language or why not

Checklist

• I have read the Auth0 general contribution guidelines
• All existing and new tests complete without errors
• All active GitHub checks have passed