ConsumoApiViaCep

public class Customer
    {
        public Customer() {
            DateCreated = DateTime.Now;
        }

        public int Id { get;  set; }
        public int AddressId { get;  set; }
        public string Name { get;  set; }
        public DateTime DateCreated { get;  set; }

        public Address Address { get;  set; }
    }


public class Address
    {
        public Address()
        {
            Customers = new List<Customer>();
        }

        public Address(string cep)
        {
            CEP = cep;
        }

        public int Id { get;  set; }
        public string CEP { get; set; }

        public IEnumerable<Customer> Customers { get; set; }
    }

public class CustomerAddressViewModel
    {
        public CustomerAddressViewModel()
        {
            Address = new AddressViewModel();
        }

        public int Id { get; set; }
        public int AddressId { get; set; }
        public string Name { get; set; }
        public DateTime DateCreated { get; set; }
        public string CEP { get; set; }
        public AddressViewModel Address { get; set; }
    }

public class CustomerViewModel
    {
        public CustomerViewModel() { }

        public int Id { get; set; }
        public int AddressId { get; set; }
        public string Name { get; set; }
        public DateTime DateCreated { get; set; }
        public AddressViewModel Address { get; set; }
    }

public class AddressViewModel
    {
        public AddressViewModel()
        {
            Customers = new List<CustomerViewModel>();
            Street = "";
            StreetFull = "";
            UF = "";
        }

        public int Id { get; set; }
        public string CEP { get; set; }
        public string Street { get; set; }
        public string StreetFull { get; set; }
        public string UF { get; set; }

        public IEnumerable<CustomerViewModel> Customers{get; set;}
    }

    [DataContract(Name = "endereco")]
    public class ViaCEP
    {
        public ViaCEP(string cep, string street, string streetFull, string uf)
        {
            CEP = cep;
            Street = street;
            StreetFull = streetFull;
            UF = uf;
        }

        [DataMember(Name = "cep")]
        public string CEP { get; set; }
        [DataMember(Name = "logradouro")]
        public string Street { get; set; }
        [DataMember(Name = "complemento")]
        public string StreetFull { get; set; }
        [DataMember(Name = "uf")]
        public string UF { get; set; }
    }

public class ViaCEPService
    {
        private readonly HttpClient _httpClient;

        public ViaCEPService()
        {
            _httpClient = new HttpClient();
        }

        public async Task<ViaCEP> GetByCEPAsync(string cep)
        {
            using (var http = new HttpClient())
            {
                var url = new Uri($"https://viacep.com.br/ws/{cep}/json");
                var result = http.GetAsync(url).GetAwaiter().GetResult();
                var resultContent = result.Content.ReadAsStringAsync().GetAwaiter().GetResult();

                return JsonConvert.DeserializeObject<ViaCEP>(resultContent);
            }
        }
    }


public class CustomerService
{
    public IEnumerable<Customer> _customerData;
    public IEnumerable<Address> _addressData;

    public CustomerService()
        {
            _addressData = new List<Address>()
                {
                    new Address{ CEP = "17052520", Id = 1, Customers = new List<Customer>{ new Customer{Id = 1}}},
                    new Address{ CEP = "44573100", Id = 2, Customers = new List<Customer>{ new Customer{Id = 2}}},
                    new Address{ CEP = "50080490", Id = 3, Customers = new List<Customer>{ new Customer{Id = 3}}}
                };

            _customerData = new List<Customer>()
                {
                    new Customer{ Id = 1, AddressId = 1, Name = "Zier Zuveiku", Address = _addressData.FirstOrDefault(x => x.Id.Equals(1))},
                    new Customer{ Id = 2, AddressId = 2, Name = "Vikehel Pleamakh", Address = _addressData.FirstOrDefault(x => x.Id.Equals(2))},
                    new Customer{ Id = 3, AddressId = 3, Name = "Diuor PleaBolosmakh", Address = _addressData.FirstOrDefault(x => x.Id.Equals(3))}
                };
        }

    public IEnumerable<Address> GetAddress() => _addressData.ToList();
    public IEnumerable<Customer> GetCustomers() => _customerData.ToList();


    public async Task<IEnumerable<CustomerAddressViewModel>> GetAllAsync()
        {

            var _viaCEPService = new ViaCEPService();

            var customers = _customerData.Select(x => new CustomerAddressViewModel {
                Id = x.Id,
                AddressId = x.AddressId,
                Name = x.Name,
                DateCreated = x.DateCreated,
                CEP = x.Address?.CEP,
                Address = new AddressViewModel{
                    Id = x.Address.Id,
                    CEP = x.Address.CEP,
                }
            }).ToList();

            foreach (var customer in customers)
            {
                var address = await _viaCEPService.GetByCEPAsync(customer.CEP);

                customer.Address.Id = customer.AddressId;
                customer.Address.Street = address?.Street;
                customer.Address.StreetFull = address?.StreetFull;
                customer.Address.UF = address?.UF;
            }

            return customers;
        }
}
void Main()
{
    var service = new CustomerService();
    var viacepservice = new ViaCEPService();
    Console.WriteLine(service.GetAllAsync());
    //Console.WriteLine(service.GetAddress());
    //Console.WriteLine(service.GetCustomers());
    //Console.WriteLine(viacepservice.GetByCEPAsync("50080490"));
}

// Define other methods and classes here