private static void RegisterTokenAuthorizationOptions(IServiceCollection services)
        {
            RSACryptoServiceProvider keyService = new RSACryptoServiceProvider(2048);

            keyService.FromXmlString(Resources.RsaProvider);
            RsaSecurityKey key = new RsaSecurityKey(keyService.ExportParameters(true));

            var tokenOptions = new TokenAuthorizationOptions
            {
                Audience           = "MobileSecondHandApp",
                Issuer             = "MarcinSzyszka",
                SigningCredentials = new SigningCredentials(key, SecurityAlgorithms.RsaSha256Signature)
            };

            services.AddSingleton <TokenAuthorizationOptions>(tokenOptions);
        }