private static JwtSecurityTokenGenerator GetTokenGenerator(
                DateTime? now = null)
            {
                var tokenGenerator = new JwtSecurityTokenGenerator();

                tokenGenerator.SetDateTimeNowFactory(() => now ?? DateTime.UtcNow);

                return tokenGenerator;
            }
            private static JwtSecurityTokenGenerator CreateSubjectUnderTest(
                JwtSecurityTokenHandler tokenHandler,
                DateTime? now = null)
            {
                var sut = new JwtSecurityTokenGenerator();

                sut.SetDateTimeNowFactory(() => now ?? DateTime.Now);
                sut.SetSecurityTokenHandlerFactory(() => tokenHandler);

                return sut;
            }